Catalysts

15 pages, 1246 KiB

Open AccessArticle

Biodiesel Production from Waste Frying Oil (WFO) Using a Biomass Ash-Based Catalyst

by Benjamín Nahuelcura, María Eugenia González, Nicolas Gutierrez, Jaime Ñanculeo and Juan Miguel Romero-García

Catalysts 2024, 14(8), 553; https://doi.org/10.3390/catal14080553 - 22 Aug 2024

Viewed by 636

Abstract

Biodiesel, an eco-friendly alternative to conventional fossil fuels, offers reduced emissions like carbon dioxide, sulfur oxides, and soot. This study explores biodiesel production from a blend of waste oils using a novel biomass-based catalyst derived from the bottom ash of a biomass boiler. [...] Read more.

Biodiesel, an eco-friendly alternative to conventional fossil fuels, offers reduced emissions like carbon dioxide, sulfur oxides, and soot. This study explores biodiesel production from a blend of waste oils using a novel biomass-based catalyst derived from the bottom ash of a biomass boiler. Catalyst synthesis involved wet impregnation, a unique approach using previously unreported bottom ash. Characterization via SEM-EDS, BET, FTIR, and XRD revealed its composition and structure. Optimization of biodiesel production involved assessing alcohol molar ratio, catalyst concentration, and reaction time, achieving a maximum FAME concentration of 95% under specific conditions. Blending residual palm oil with waste frying oil enhanced biodiesel properties, demonstrating a maximum FAME concentration at specific catalyst concentration (8%), molar ratio (1:10), and reaction time (2 h). Catalyst reusability, up to three cycles without significant yield variation, showcased its sustainability. The catalyst, primarily composed of calcium, a characteristic biomass bottom ash component, exhibited mesoporous features. Impregnation with eggshells not only altered composition but also ensured a uniform particle size distribution. FTIR and XRD analyses indicated calcium in hydroxide and crystallized forms. Effective catalyst separation methods included decanting or water washing, with optimal biodiesel purity achieved through 3% phosphoric acid washing at 60 °C. Various recovery methods were assessed, highlighting hexane washing as the most efficient, enabling up to three catalyst reuse cycles without substantial efficiency loss. Full article

(This article belongs to the Topic Catalysis for Sustainable Chemistry and Energy, 2nd Volume)

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40 pages, 4101 KiB

Open AccessFeature PaperReview

Properties, Industrial Applications and Future Perspectives of Catalytic Materials Based on Nickel and Alumina: A Critical Review

by Guido Busca, Elena Spennati, Paola Riani and Gabriella Garbarino

Catalysts 2024, 14(8), 552; https://doi.org/10.3390/catal14080552 - 22 Aug 2024

Viewed by 633

Abstract

The bulk and surface properties of materials based on nickel and aluminum oxides and hydroxides, as such or after reduction processes, are reviewed and discussed critically. The actual and potential industrial applications of these materials, both in reducing conditions and in oxidizing conditions, [...] Read more.

The bulk and surface properties of materials based on nickel and aluminum oxides and hydroxides, as such or after reduction processes, are reviewed and discussed critically. The actual and potential industrial applications of these materials, both in reducing conditions and in oxidizing conditions, are summarized. Mechanisms for reactant molecule activation are also discussed. Full article

(This article belongs to the Special Issue Feature Papers in "Industrial Catalysis" Section)

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XRD patterns of γ-Al2O3 and 20 wt% and 50 wt% loaded NiO/Al2O3, prepared by impregnation. Arrows are the positions of the peaks of NiO (bunsenite). CoKα radiation. Full article ">Figure 2
FTIR skeletal spectra (KBr pressed disks) of γ-Al2O3 and 5 wt%, 20 wt% and 50 wt% loaded NiO/Al2O3, prepared by impregnation, as compared with those of NiAl2O4 and NiO (bunsenite). Full article ">Figure 3
Visible and near infrared spectra of NiO, NiAl2O4 and 20 wt% NiO/Al2O3 “monolayer” catalyst. Full article ">Figure 4
Field Emission Scanning Electron Microscopy image of bulk nickel (ex-NiO) after CO2 hydrogenation experiment. Carbonaceous matter is evident, mainly encapsulating the brighter Ni metal particles. Full article ">Figure 5
Field Emission Scanning Electron Microscopy image of a Ni/Al2O3-based catalyst (16% Ni) after ethanol steam reforming experiment (right). Carbonaceous matter is evident, mainly carbon nanotubes that contain some bright nickel particles in the interior. Full article ">Figure 6
Typical H2-TPR curves for samples in the NiO-Al2O3 system. Full article ">Figure 7
IR spectra of low-temperature adsorption of CO on patterns of γ-Al2O3 (top) and 20 wt% NiO/Al2O3, prepared by impregnation, oxidized (middle) and reduced (below). Bands at 2211, 2202 and 2188–2195 cm−1 are due to CO interacting with Al3+ ions. The band at 2183–2195 cm−1 is due to CO interacting with Ni2+. The bands at 2129, 2059, 2044 and 2020 cm−1 are due to polycarbonyls of dispersed Ni0. The band shifting from 2098 cm−1 to lower frequencies by decreasing coverage is due to terminal monocarbonyls over Ni metal particle surfaces. Full article ">Figure 8
FE-SEM micrographs of spent Ni/Al2O3 catalysts after prereduction and CO2 methanation experiments, recorded using backscattered electrons. Left: 16% Ni (20 wt% NiO) loading; right: 39% (50 wt% NiO) Ni loading. Bright particles are Ni metal particles. Full article ">

23 pages, 5014 KiB

Open AccessArticle

Design and Performance of CuNi-rGO and Ag-CuNi-rGO Composite Electrodes for Use in Fuel Cells

by Mohamed Shaban, Aya Mohamed, Mohamed G. M. Kordy, Hamad AlMohamadi, M. F. Eissa and Hany Hamdy

Catalysts 2024, 14(8), 551; https://doi.org/10.3390/catal14080551 - 22 Aug 2024

Viewed by 474

Abstract

This work developed new electrocatalysts for direct alcohol oxidation fuel cells (DAFCs) by using graphene and reduced graphene oxides (GO and rGO) as supporting nanomaterials for copper–nickel (CuNi) nanocomposites. The manufacture of CuNi, CuNi-GO, and CuNi-rGO nanocomposites was realized through the adaptation of [...] Read more.

This work developed new electrocatalysts for direct alcohol oxidation fuel cells (DAFCs) by using graphene and reduced graphene oxides (GO and rGO) as supporting nanomaterials for copper–nickel (CuNi) nanocomposites. The manufacture of CuNi, CuNi-GO, and CuNi-rGO nanocomposites was realized through the adaptation of Hummer’s method and hydrothermal techniques, with subsequent analysis using a range of analytical tools. The electrocatalytic behavior of these materials in DAFCs, with methanol and ethanol as the fuels, was scrutinized through various methods, including cyclic voltammetry, linear sweep, chronoamperometry, and electrochemical impedance spectroscopy. This investigation also assessed the stability and charge transfer dynamics. The rGO-based CuNi nanocomposite demonstrated a remarkable performance boost, showing increases of approximately 319.6% for methanol and 252.6% for ethanol oxidation compared to bare CuNi. The integration of silver nanoparticles into the Ag-CuNi-rGO electrode led to a current density surge to 679.3 mA/g, which signifies enhancements of 254.2% and 812.6% relative to the CuNi-rGO and CuNi electrodes, respectively. These enhancements are ascribed to the augmented densities of hot sites and the synergistic interactions within the nanocatalysts. The findings underscore the potential of Ag and rGO as effective supports for CuNi nanocomposites, amplifying their catalytic efficiency in DAFC applications. Full article

(This article belongs to the Section Nanostructured Catalysts)

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12 pages, 7415 KiB

Open AccessArticle

Photoinduced Mechanisms of C–S Borylation of Methyl(p-tolyl)Sulfane with Bis(Pinacolato)diboron: A Density Functional Theory Investigation

by Yuxiao Ming, Tiantian Feng, Bin Chen and Dagang Zhou

Catalysts 2024, 14(8), 550; https://doi.org/10.3390/catal14080550 - 22 Aug 2024

Viewed by 331

Abstract

The reaction mechanisms of C–S borylation of aryl sulfides catalyzed with 1,4-benzoquinone (BQ) were investigated by employing the M06-2X-D3/ma-def2-SVP method and basis set. In this study, the SMD model was taken to simulate the solvent effect of 1,4-dioxane. Also, TD-DFT calculations of BQ [...] Read more.

The reaction mechanisms of C–S borylation of aryl sulfides catalyzed with 1,4-benzoquinone (BQ) were investigated by employing the M06-2X-D3/ma-def2-SVP method and basis set. In this study, the SMD model was taken to simulate the solvent effect of 1,4-dioxane. Also, TD-DFT calculations of BQ and methyl(p-tolyl)sulfane were performed in an SMD solvent model. The computational results indicated that BQ and methyl(p-tolyl)sulfane, serving as a photo-catalyst, would be excited under a blue LED of 450 nm, aligning well with experimental observations. Additionally, the role of ³O₂ was investigated, revealing that it could be activated into ¹O₂ from the released energy of ¹[BQ + methyl(p-tolyl)sulfane]* or ³[BQ + methyl(p-tolyl)sulfane]*→BQ + methyl(p-tolyl)sulfane process. Then, ¹O₂, bis(pinacolato)diboron, and methyl(p-tolyl)sulfane would, through a series of reactions, yield the final product, P. The Gibbs free energy surface shows that path a2-2 is optimal, and this path has fewer steps and a lower energy barrier. Electron spin density isosurface graphs were employed to analyze the structures and elucidate the single electron distribution. These computational results offer valuable insights into the studied interactions and related processes and shed light on the mechanisms governing C–S borylation from aryl sulfides and b₂pin₂ catalyzed with BQ and methyl(p-tolyl)sulfane. Full article

(This article belongs to the Section Photocatalysis)

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Full article ">Figure 1
Frontier molecular orbital of BQ and R1 + BQ models. Full article ">Figure 2
The ρhole (blue) and ρele (green) of S0→S1, S0→S2, and S0→S3 of R1 + BQ. Full article ">Figure 3
The Gibbs free energy surfaces in photocatalysis process. Full article ">Figure 4
The Gibbs free energy surfaces of Paths a1-1, a1-2, and a1-3. Full article ">Figure 5
The electron spin density isosurface graphs of some structures in Path a1 and a2. Full article ">Figure 6
The Gibbs free energy surfaces from IM1 to P via probable Path a2-1. Full article ">Figure 7
The Gibbs free energy surfaces from IM1 to P via probable Path a2-2. Full article ">Scheme 1
C–S borylation of aryl sulfides. Full article ">Scheme 2
The total reaction from R1 + R2→P. Full article ">Scheme 3
The detailed reaction photocatalysis process. Full article ">Scheme 4
The detailed reaction process from IM1 to P via two probable Paths, a2-1 and a2-2. Full article ">

14 pages, 6272 KiB

Open AccessArticle

Biodiesel Synthesis from Coconut Oil Using the Ash of Citrus limetta Peels as a Renewable Heterogeneous Catalyst

by Priyal Kaushik, Gurmeet Kaur and Imran Hasan

Catalysts 2024, 14(8), 549; https://doi.org/10.3390/catal14080549 - 22 Aug 2024

Viewed by 567

Abstract

The synthesis of biodiesel can be achieved using either homogeneous or heterogeneous catalysts. Given the non-renewable nature of homogeneous catalysts, heterogeneous catalysts are increasingly preferred for biodiesel production. Agricultural wastes serve as a viable source for these heterogeneous catalysts, contributing to environmental sustainability. [...] Read more.

The synthesis of biodiesel can be achieved using either homogeneous or heterogeneous catalysts. Given the non-renewable nature of homogeneous catalysts, heterogeneous catalysts are increasingly preferred for biodiesel production. Agricultural wastes serve as a viable source for these heterogeneous catalysts, contributing to environmental sustainability. This study introduces a novel, eco-friendly, cost-effective, and efficient heterogeneous catalyst that was developed and derived from Citrus limetta peels for biodiesel production. The catalyst was thoroughly characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffractograms (XRD), Field Emission Scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX). Coconut oil, a rich and renewable resource, was used as the feedstock for the biodiesel synthesis. The conversion process was confirmed by ¹H NMR, IR spectra, mass spectra, and ¹³C NMR of the biodiesel. The developed method using the Citrus limetta peel-derived catalyst demonstrated a 100% yield. The results show the optimum conditions for biodiesel synthesis are 1 w/v (for the catalytical dose), with a 6:1 methanol/oil ratio at 60 °C for 3 h. The synthesized biodiesel exhibited a high cetane value of 54, contributing to improved ignition and reduced engine noise. Its sulfur-free composition, boiling point of 294 °C, high viscosity of 2.5 mm²/s, acid value of 0.09 mgKOH/g, and flash point of 142 °C enhance its environmental profile. The catalyst can be used for up to five cycles, underscoring its potential as a cost-effective and sustainable approach for biodiesel production. Full article

(This article belongs to the Special Issue Novel Materials for Heterogeneous Catalysis and Energy Conversion)

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14 pages, 4486 KiB

Open AccessArticle

Efficient and Robust Photodegradation of Dichlorvos Pesticide by BiOBr/WO_2.72 Nanocomposites with Type-I Heterojunction under Visible Light Irradiation

by Aoyun Meng, Wen Li, Zhen Li and Jinfeng Zhang

Catalysts 2024, 14(8), 548; https://doi.org/10.3390/catal14080548 - 21 Aug 2024

Viewed by 463

Abstract

In this study, we developed novel BiOBr/WO_2.72 nanocomposites (abbreviated as BO/WO) and systematically investigated their photocatalytic degradation performance against the pesticide dichlorvos under visible light irradiation. The experimental results demonstrated that the BO/WO nanocomposites achieved an 85.4% degradation of dichlorvos within 80 [...] Read more.

In this study, we developed novel BiOBr/WO_2.72 nanocomposites (abbreviated as BO/WO) and systematically investigated their photocatalytic degradation performance against the pesticide dichlorvos under visible light irradiation. The experimental results demonstrated that the BO/WO nanocomposites achieved an 85.4% degradation of dichlorvos within 80 min. In comparison, the BO alone achieved a degradation degree of 66.8%, and the WO achieved a degradation degree of 64.7%. Furthermore, the BO/WO nanocomposites retained 96% of their initial activity over five consecutive cycles, demonstrating exceptional stability. Advanced characterization techniques, such as high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) confirmed the composition and catalytic mechanism of the composite material. The findings indicated that the BO/WO nanocomposites, through their optimized Type-I heterojunction structure, achieved efficient separation and transport of photogenerated electron–hole pairs, significantly enhancing the degree of degradation of organophosphate pesticides. This research not only propels the development of high-performance photocatalytic materials, but also provides innovative strategies and a robust scientific foundation for mitigating global organophosphate pesticide pollution, underscoring its substantial potential for environmental remediation. Full article

(This article belongs to the Special Issue Applications of Catalytic Reactions in Promoting the Health of Organisms)

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6 pages, 1865 KiB

Open AccessEditorial

Fifty Years of Research in Environmental Photocatalysis: Scientific Advances, Discoveries, and New Perspectives

by Chantal Guillard and Didier Robert

Catalysts 2024, 14(8), 547; https://doi.org/10.3390/catal14080547 - 21 Aug 2024

Viewed by 630

Abstract

The concept of “photocatalysis” was discovered at the beginning of the twentieth century, and research in this area has especially intensified over the past 50 years [...] Full article

(This article belongs to the Special Issue 50 Years of Research in Photocatalysis: Scientific Advances, Discoveries and New Perspectives)

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12 pages, 2695 KiB

Open AccessArticle

Impact of Oxygen-Containing Groups on Pd/C in the Catalytic Hydrogenation of Acetophenone and Phenylacetylene

by Pengyao You, Liming Wu, Lu Zhou, Yong Xu and Ruixuan Qin

Catalysts 2024, 14(8), 545; https://doi.org/10.3390/catal14080545 - 21 Aug 2024

Viewed by 552

Abstract

Pd/C catalysts play a pivotal role in contemporary chemical industries due to their exceptional performance in diverse hydrogenation processes and organic reactions. Over the past century, researchers have extensively explored the factors influencing Pd/C catalyst performance, particularly emphasizing the impact of oxygen-containing groups [...] Read more.

Pd/C catalysts play a pivotal role in contemporary chemical industries due to their exceptional performance in diverse hydrogenation processes and organic reactions. Over the past century, researchers have extensively explored the factors influencing Pd/C catalyst performance, particularly emphasizing the impact of oxygen-containing groups through oxidation or reduction modifications. However, most studies use respective Pd/C catalysts to analyze the catalytic reactions of one or a class of chemical bonds (polar or non-polar). This study investigates alterations in Pd/C catalysts during temperature-programmed reduction (TPR) and evaluates the hydrogenation activity of unsaturated polar bonds (C=O, acetophenone) and non-polar bonds (C≡C, phenylacetylene) in Pd/C catalysts. The experimental results indicate that the reduction of Pd/C decreases the content of oxygen-containing groups, reducing hydrogenation activity for acetophenone but increasing it for phenylacetylene. This research highlights the preference of regular Pd surfaces for non-polar bond reactions and the role of Pd/oxide sites in facilitating polar bond hydrogenation. These discoveries offer essential insights into how oxygen-containing groups influence catalytic performance and allow us to propose potential avenues for enhancing the design and production of Pd/C catalysis. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis for Selective Hydrogenation)

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The TPR-MS signals of the Pd/C catalyst recorded in 5% H2/Ar. Full article ">Figure 2
(a–c) TEM images and (d–f) particle size distribution statistics for 60 °C-H2-Pd/C, 500 °C-TPR-Pd/C, and 800 °C-TPR-Pd/C, respectively. Full article ">Figure 3
(a) XRD of initial Pd/C, 60 °C-H2-Pd/C, 500 °C-TPR-Pd/C, and 800 °C-TPR-Pd/C. (b) CO-DRIFTS of 60 °C-H2-Pd/C and 500 °C-TPR-Pd/C. Prior to CO-DRIFTS collection, the sample was purged successively with Ar, 5% CO/Ar, and Ar for 10 min each. Full article ">Figure 4
Mathematical relationship between particle diameter and activity of a regular polyhedron. (a) FCC, regular tetrahedron; (b) FCC, regular octahedron; (c) FCC, cube; (d) BCC, cube. FCC: Face Center Cubic; BCC: Body Center Cubic. Full article ">Figure 5
Catalytic performance of 60 °C-H2-Pd/C, 500 °C-TPR-Pd/C, and 800 °C-TPR-Pd/C. Hydrogenation of acetophenone: (a) catalytic activity, (b) turnover frequency (TOF), and (c) analysis of activity related to particle size. Hydrogenation of phenylacetylene: (d) catalytic activity, (e) TOF, and (f) analysis of activity related to particle size. Reaction conditions: 60 °C, 1 bar H2, 5 mL ethanol, n(acetophenone):n(Pd) = 500:1; n(phenylacetylene):n(Pd) = 2000:1. k = TOF = (the molar of substrates conversion)/(the molar of Pd on the surface)/(conversion time). Full article ">

14 pages, 4821 KiB

Open AccessArticle

Research on Cu-Site Modification of g-C₃N₄/CeO₂-like Z-Scheme Heterojunction for Enhancing CO₂ Reduction and Mechanism Insight

by Yiying Zhou, Junxi Cai, Yuming Sun, Shuhan Jia, Zhonghuan Liu, Xu Tang, Bo Hu, Yue Zhang, Yan Yan and Zhi Zhu

Catalysts 2024, 14(8), 546; https://doi.org/10.3390/catal14080546 - 20 Aug 2024

Viewed by 373

Abstract

In this work, the successful synthesis of a Cu@g-C₃N₄/CeO₂-like Z-scheme heterojunction through hydrothermal and photo-deposition methods represents high CO₂ reduction activity with remarkable CO selectivity, as evidenced by the impressive CO yield of 33.8 [...] Read more.

In this work, the successful synthesis of a Cu@g-C₃N₄/CeO₂-like Z-scheme heterojunction through hydrothermal and photo-deposition methods represents high CO₂ reduction activity with remarkable CO selectivity, as evidenced by the impressive CO yield of 33.8 μmol/g for Cu@g-C₃N₄/CeO₂, which is over 10 times higher than that of g-C₃N₄ and CeO₂ individually. The characterization and control experimental results indicate that the formation of heterojunctions and the introduction of Cu sites promote charge separation and the transfer of hot electrons, as well as the photothermal effect, which are the essential reasons for the improved CO₂ reduction activity. Remarkably, Cu@g-C₃N₄/CeO₂ still exhibits about 92% performance even after multiple cycles. In situ FTIR was utilized to confirm the production of COOH* at 1472 cm⁻¹ and to elucidate the mechanism behind the high selectivity for CO production. The study’s investigation into the wide-ranging applicability of the Cu@g-C₃N₄/CeO₂-like Z-scheme heterojunction catalysts is noteworthy, and the exploration of potential reaction mechanisms for CO2 reduction adds valuable insights to the field of catalysis. Full article

(This article belongs to the Special Issue Mineral-Based Composite Catalytic Materials)

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Structures of monolayer CeO2 (a), g-C3N4 (b), Cu@g-C3N4/CeO2 (c). Full article ">Figure 2
TEM images of the g-C3N4 (a), CeO2 (b), Cu@g-C3N4/CeO2 (c), SEM images of g-C3N4 (d), CeO2 (e), Cu@g-C3N4/CeO2 (f), EDX mapping of Cu@g-C3N4/CeO2 (g1–g5). Full article ">Figure 3
XRD patterns (a), XPS survey spectra (b) of g-C3N4, CeO2 and Cu@g-C3N4/CeO2, high resolution of C1s of g-C3N4 and Cu@g-C3N4/CeO2(c), O1s XPS spectra of CeO2 and Cu@g-C3N4/CeO2 (d), N1s XPS spectra of g-C3N4 and Cu@g-C3N4/CeO2 (e), Ce 3d XPS spectra of CeO2 and Cu@g-C3N4/CeO2 (f). Full article ">Figure 4
PL spectra (a), FL spectra (b), UV–Vis DRS (c), transient photocurrent response (d) and EIS Nyquist plots (e) of g-C3N4 and CeO2 and Cu@g-C3N4/CeO2, Mott–Schottky (f) of Cu@g-C3N4/CeO2. Full article ">Figure 5
CO yields with condensed water ((a), Xenon lamp, 1000 mW/cm2, 6 °C); the CO yields over g-C3N4 and CeO2 and Cu@g-C3N4/CeO2 hybrids without condensed water ((b), Xenon lamp, 1000 mW/cm2); the recycling test for CO2 reduction using Cu@g-C3N4/CeO2 without condensed water ((c), Xenon lamp, 1000 mW/cm2). Full article ">Figure 6
(a) XRD comparison of photocatalysis before and after photocatalysis; (b) Evolution of CO after 4 h of reaction under various reaction conditions. In the case of N2, no light, normal and without photocatalyst, respectively. Full article ">Figure 7
In situ FTIR spectra of CO2 adsorption (a) and reaction (b) of Cu@g-C3N4/CeO2 collected at different time intervals. Full article ">Figure 8
Schematic diagram of the mechanism of CO2 reduction by Cu@g-C3N4/CeO2 under visible light irradiation. Full article ">

18 pages, 3457 KiB

Open AccessFeature PaperArticle

Influence of UV-A Light Modulation on Phenol Mineralization by TiO₂ Photocatalytic Process Coadjuvated with H₂O₂

by Nicola Morante, Luca De Guglielmo, Nunzio Oliva, Katia Monzillo, Nicola Femia, Giulia Di Capua, Vincenzo Vaiano and Diana Sannino

Catalysts 2024, 14(8), 544; https://doi.org/10.3390/catal14080544 - 20 Aug 2024

Viewed by 656

Abstract

This work examined the influence of UV-A light modulation on the photocatalytic process coadjuvated with H₂O₂ to mineralize phenol in an aqueous solution. A fixed-bed batch photocatalytic reactor with a flat-plate geometry, irradiated by UV-A LEDs, was employed. The successful [...] Read more.

This work examined the influence of UV-A light modulation on the photocatalytic process coadjuvated with H₂O₂ to mineralize phenol in an aqueous solution. A fixed-bed batch photocatalytic reactor with a flat-plate geometry, irradiated by UV-A LEDs, was employed. The successful deposition of commercial TiO₂ PC105 on a steel plate (SP) was achieved, and the structured photocatalyst was characterized using Raman spectroscopy, specific surface area (SSA) measurements, and UV–vis DRS analysis. These analyses confirmed the formation of a titania coating in the anatase phase with a bandgap energy of 3.25 eV. Various LED-dimming techniques, with both fixed and variable duty cycle values, were tested to evaluate the stability of the photocatalyst’s activity and the influence of operating parameters during the mineralization of 450 mL of a phenol solution. The optimal operating parameters were identified as an initial phenol concentration of 10 ppm, a hydrogen peroxide dosage of 0.208 g L⁻¹, and triangular variable duty cycle light modulation. Under these conditions, the highest apparent phenol degradation kinetic constant (0.39 min⁻¹) and the total mineralization were achieved. Finally, the energy consumption for mineralizing 90% phenol in one cubic meter of treated water was determined, showing the greatest energy savings with triangular light modulation. Full article

(This article belongs to the Special Issue Commemorative Special Issue for Prof. Dr. Dion Dionysiou)

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12 pages, 3035 KiB

Open AccessFeature PaperArticle

Dual-Enzyme-Cascade Catalysis for PET Biodegradation Based on a Variable-Temperature Program

by Dong Lu, Jinglong Wu, Shuming Jin, Qiuyang Wu, Fang Wang, Li Deng and Kaili Nie

Catalysts 2024, 14(8), 543; https://doi.org/10.3390/catal14080543 - 20 Aug 2024

Viewed by 967

Abstract

As an environmentally friendly technology, enzymatic degradation of waste polyethylene terephthalate (PET) has great application potential. Mono (hydroxyethyl) terephthalate (MHET), an intermediate product of PET degradation, accumulates during the degradation process. MHET reduces the activity of PETase and influences further enzymatic degradation. The [...] Read more.

As an environmentally friendly technology, enzymatic degradation of waste polyethylene terephthalate (PET) has great application potential. Mono (hydroxyethyl) terephthalate (MHET), an intermediate product of PET degradation, accumulates during the degradation process. MHET reduces the activity of PETase and influences further enzymatic degradation. The combined catalysis of MHETase and PETase is an effective strategy to solve this problem. However, the difference in thermostability between MHETase and PETase limits their combination. In our previous study, a PETase of muEst1 exhibited acceptable PET-degradation ability, but the abundant MHET accumulation in its degradation products limited its further application. In this study, MHETases with good thermostability were screened for combination with muEst1 for the cascade reaction of PET degradation, and a two-stage variable-temperature program was developed. The results of this investigation show that this approach results in a PET-degradation rate of 92.71% with a terephthalic acid content above 85.9%. This investigation provides an alternative method for scaled-up enzymatic PET degradation. Full article

(This article belongs to the Section Biocatalysis)

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Biodegradation of particles of a post-consumer commercial PET bottle. Product concentrations and degradation rates at 3‰ (A), 3% (B), and 5% (C) muEst1 dosages. Full article ">Figure 2
SDS-PAGE of different hydrolases: (A) supernatant of the expression cell culture. (B) pellet of the expression cell culture. Lane 1: muEst1, lane 2: KLMHETase, lane 3: BsMHETase, lane 4: TtMHETase, lane 5: IsMHETase, lane 6: KL_muEst1, lane 7: Bs_muEst1, lane 8: Tt_muEst1, lane 9: Is-muEst1. The individual and fusion protein sizes were as follows: muEst1 29.4 kDa, KLMHETase 28.5 kDa, BsMHETase 54.4 kDa, TtMHETase 26.4 kDa, IsMHETase 63.8 kDa, KL_muEst1 60.1 kDa, Bs_muEst1 86.1 kDa, Tt_muEst1 58.1 kDa, and Is_muEst1 98.5 kDa. IsMHETase--MHETase from Ideonella sakaiensis, KLMHETase--redesigned from thermophilic carboxylesterase Est30 (Geobacillus stearothermophilus), TtMHETase--MHETase from Thermus thermophilus, and BsMHETase--MHETase from Bacillus subtilis. Full article ">Figure 3
The results of PET degradation by combinations of muEst1 and MHETases. (A) PET degradation at 50 °C for 8 h; (B) PET degradation at 65 °C for 8 h; (C) PET degradation at 50 °C for 24 h; (D) PET degradation at 65 °C for 24 h; (E) thermostability of enzymes at 50 °C and 65 °C; (F) comparison of enzymatic activity. Full article ">Figure 4
PET degradation by fusion proteins. Full article ">Figure 5
PET degradation by the three-stage process. (A) Scheme of the three-stage process; (B) Comparison of PET degradation by different processes; (C) Analysis of product composition and release. Full article ">Figure 6
PET degradation in the two-stage process. (A) Scheme of the two-stage process; (B) Product release in the single-enzyme muEst1 samples; (C) Product release in the dual-enzyme samples. Full article ">Figure 7
PET degradation in a 5 L bioreactor. Full article ">

14 pages, 3798 KiB

Open AccessFeature PaperArticle

Oxidation in Flow Using an Ionic Immobilized TEMPO Catalyst on an Ion Exchange Resin

by Johannes Gmeiner and Gerrit A. Luinstra

Catalysts 2024, 14(8), 542; https://doi.org/10.3390/catal14080542 - 19 Aug 2024

Viewed by 452

Abstract

An ionic heterogenized catalyst system for Anelli oxidation has been developed using potassium 4-sulfonato-oxy-2,2,6,6-tetramethylpiperidine-1-yloxyl (TEMPO-4-sulfate) and anion exchange beads as support material. The catalytic oxidation of benzyl alcohol by bis(acetoxy)iodobenzene (BAIB) in acetonitrile with the modified beads gives a 94% yield of benzaldehyde [...] Read more.

An ionic heterogenized catalyst system for Anelli oxidation has been developed using potassium 4-sulfonato-oxy-2,2,6,6-tetramethylpiperidine-1-yloxyl (TEMPO-4-sulfate) and anion exchange beads as support material. The catalytic oxidation of benzyl alcohol by bis(acetoxy)iodobenzene (BAIB) in acetonitrile with the modified beads gives a 94% yield of benzaldehyde within 60 min (batch operation). The beads give about the same conversion of benzyl alcohol in six consecutive cycles when reused after simple washing, albeit with a somewhat longer half-life time. The TEMPO entity could be removed from the beads using a sodium chloride/sodium hydroxy mixture. Reloading the beads with TEMPO-4-sulfate restored about 80% of their initial catalytic action. This exemplifies that the catalytic activity in a fixed bed can be regained without the need for cleaning and repacking the reactor. Preliminary experiments in a fixed bed show that a constant benzyl alcohol conversion of 84% over 10 residence times (as plug flow) can be achieved by the in-flow execution of the oxidation reaction. Full article

(This article belongs to the Special Issue Design, Synthesis and Applications of Homogeneous/Heterogeneous Oxidation Catalysts)

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15 pages, 4832 KiB

Open AccessArticle

Cu/MgO as an Efficient New Catalyst for the Non-Oxidative Dehydrogenation of Ethanol into Acetaldehyde

by Chao Tian, Yinghong Yue, Changxi Miao, Weiming Hua and Zi Gao

Catalysts 2024, 14(8), 541; https://doi.org/10.3390/catal14080541 - 19 Aug 2024

Viewed by 435

Abstract

The non-oxidative dehydrogenation of ethanol into acetaldehyde is one of the efficient solutions for biomass upgrading. In this work, a series of copper catalysts supported on MgO with different Cu loadings ranging from 2.5% to 20% were prepared by an impregnation method. The [...] Read more.

The non-oxidative dehydrogenation of ethanol into acetaldehyde is one of the efficient solutions for biomass upgrading. In this work, a series of copper catalysts supported on MgO with different Cu loadings ranging from 2.5% to 20% were prepared by an impregnation method. The as-synthesized Cu/MgO catalysts were characterized by N₂ adsorption, XRD, TEM, CO₂-TPD, XPS and TPR. These catalysts were found to be effective for ethanol dehydrogenation into acetaldehyde. As the Cu loading was increased, the ethanol conversion first increased and then leveled off. At a WHSV of 1.5 h⁻¹ and 250 °C, the 20%Cu/MgO catalyst gave an initial conversion of 81.5%, with 97.7% selectivity toward acetaldehyde. Compared to 20%Cu/SiO₂, the 20%Cu/MgO catalyst displayed an equivalent initial acetaldehyde yield, higher acetaldehyde selectivity and longer stability. Full article

(This article belongs to the Special Issue Catalytic Conversion of Renewable Biomass Platform Molecules)

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20 pages, 5431 KiB

Open AccessArticle

Catalytic Ozonation of Sulfachloropyridazine Sodium by Diatomite-Modified Fe₂O₃: Mechanism and Pathway

by Yang Yu, Lingling Wang, Zhandong Wu, Xuguo Liu, Zhen Liu, Lijian Zhang and Lixin Li

Catalysts 2024, 14(8), 540; https://doi.org/10.3390/catal14080540 - 19 Aug 2024

Viewed by 462

Abstract

A diatomite-modified Fe₂O₃ (Fe₂O₃/Dia) catalyst was prepared to catalyze the ozonation degradation of sulfachloropyridazine sodium (SPDZ). The chemical oxygen demand (COD) was used as the index of pollutant degradation. The catalytic ozonation experiment showed that the [...] Read more.

A diatomite-modified Fe₂O₃ (Fe₂O₃/Dia) catalyst was prepared to catalyze the ozonation degradation of sulfachloropyridazine sodium (SPDZ). The chemical oxygen demand (COD) was used as the index of pollutant degradation. The catalytic ozonation experiment showed that the COD removal rate of SPDZ was 87% under Fe₂O₃/Dia catalysis, which was much higher than that obtained when using Fe₂O₃ as the catalyst. The characteristics of the Fe₂O₃/Dia catalyst were investigated, and the successful synthesis of the Fe₂O₃/Dia composite catalyst was proved by XRD, XPS, SEM, FTIR, BET and other characterization methods. The catalytic mechanism of degradation by ozone with Fe₂O₃/Dia was analyzed. According to free-radical trapping experiments and an in situ electron paramagnetic spectrometer characterization analysis, the main oxidizing species in the catalytic Fe₂O₃/Dia ozone system is ·OH. The intermediates in the degradation process of SPDZ were detected and analyzed in detail by liquid chromatography-coupled mass spectrometry. The degradation mechanism and three degradation paths of SPDZ were proposed. Full article

(This article belongs to the Section Environmental Catalysis)

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14 pages, 5631 KiB

Open AccessArticle

Strengthened Removal of Tetracycline by a Bi/Ni Co-Doped SrTiO₃/TiO₂ Composite under Visible Light

by Weifang Chen, Na Zhao, Mingzhu Hu, Xingguo Liu and Baoqing Deng

Catalysts 2024, 14(8), 539; https://doi.org/10.3390/catal14080539 - 19 Aug 2024

Viewed by 410

Abstract

A two-step hydrothermal method was used to first obtain a SrTiO₃/TiO₂ composite then to dope the composite with Bi, Ni and Bi/Ni. Morphology, crystalline structures, surface valances and optical features of SrTiO₃/TiO₂ and Bi-, Ni-, Bi/Ni-doped SrTiO [...] Read more.

A two-step hydrothermal method was used to first obtain a SrTiO₃/TiO₂ composite then to dope the composite with Bi, Ni and Bi/Ni. Morphology, crystalline structures, surface valances and optical features of SrTiO₃/TiO₂ and Bi-, Ni-, Bi/Ni-doped SrTiO₃/TiO₂ were assessed. XRD and XPS analysis showed that Bi and Ni were successfully doped and existed in Bi(3+) and Ni(2+) oxidation state. UV–vis analysis further revealed that the bandgap energies of TiO₂ and SrTiO₃/TiO₂ were calculated to be 3.14 eV and 3.04 eV. By comparison, Bi, Ni and Bi/Ni doping resulted in the narrowing of bandgaps to 2.82 eV, 2.96 eV and 2.69 eV, respectively. The removal ability of SrTiO₃/TiO₂ and doped SrTiO₃/TiO₂ were investigated with tetracycline as the representative pollutant. After 40 min of exposure to visible light, Bi/Ni co-doped SrTiO₃/TiO₂ photocatalyst was able to remove 90% of the tetracycline with a mineralization rate of about 70%. In addition, first-order removal rate constant was 0.0074 min⁻¹ for SrTiO₃/TiO₂ and increased to 0.0278 min⁻¹ after co-doping. The strengthened removal by co-doped photocatalyst was attributed mainly to the enhanced absorption of visible light as co-doping resulted in the decreases of bandgap energies. At the same time, the co-doped material was robust against changes in pH. Removal of tetracycline was stable as pH changed from 5 to 9. Tetracycline removal was inhibited to a certain degree by the presence of nitrate, phosphate and high concentration of humic acid. Moreover, the co-doped material exhibited strong structural stability and reusability. In addition, a photocatalysis mechanism with photogenerated holes and ·O₂⁻ radicals as main oxidative species was proposed based on entrapping experiments and EPR results. Full article

(This article belongs to the Special Issue Recent Advances in Photocatalytic Degradation of Tetracycline Antibiotics)

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SEM images of the photocatalysts: (a) TiO2; (b)S-TO; (c) Bi/S-TO; (d) Ni/S-TO; (e) Bi/Ni/S-TO. Full article ">Figure 2
(a) XRD pattern (b) Locally enlarged XRD patterns of TiO2, S-TO, Bi/S-TO, Ni-S-TO and Bi/Ni/S-TO. Full article ">Figure 3
XPS Spectra: (a) Bi/Ni/S-TO; (b) O 1s; (c) Ti 2p; (d) Sr 3d; (e) Bi 4f; (f) Ni 2p. Full article ">Figure 3 Cont.
XPS Spectra: (a) Bi/Ni/S-TO; (b) O 1s; (c) Ti 2p; (d) Sr 3d; (e) Bi 4f; (f) Ni 2p. Full article ">Figure 4
(a) UV–vis absorption spectra of TiO2, S-TO, Bi/S-TO, Ni-S-TO and Bi/Ni/S-TO and (b) bandgap energies of TiO2 and Bi/Ni/S-TO. Full article ">Figure 5
Tetracycline removal: (a) Comparison of photocatalyst; (b) Effects of dosage; (c) Effects of initial pH; (d) Effects of co-existing anion; (e) Effects of co-existing humic acid; (f) Mineralization; (g) Stability and reusability; (h) XRD spectra. Full article ">Figure 6
(a) Free radical trapping (b) EPR signal of DMPO-·O2− and (c) EPR signal of TEMPO-h+. Full article ">Figure 7
(a) VB-XPS spectrum of Bi/Ni/S-TO. (b) Possible reaction mechanism of tetracycline removal by Bi/Ni/S-TO. Full article ">

25 pages, 3741 KiB

Open AccessReview

Exploring Intermetallic Compounds: Properties and Applications in Catalysis

by Zhiquan Hou, Mengwei Hua, Yuxi Liu, Jiguang Deng, Xin Zhou, Ying Feng, Yifan Li and Hongxing Dai

Catalysts 2024, 14(8), 538; https://doi.org/10.3390/catal14080538 - 18 Aug 2024

Viewed by 814

Abstract

Intermetallic compounds (IMCs) have attracted significant attention in recent years due to their unique properties and potential applications in various fields, particularly in catalysis. This review aims to provide an in-depth understanding of IMCs, including their synthesis methods, structural characteristics, and diverse catalytic [...] Read more.

Intermetallic compounds (IMCs) have attracted significant attention in recent years due to their unique properties and potential applications in various fields, particularly in catalysis. This review aims to provide an in-depth understanding of IMCs, including their synthesis methods, structural characteristics, and diverse catalytic applications. The review begins with an introduction to IMCs, highlighting their distinct features and advantages over traditional catalyst materials. It then delves into the synthesis techniques employed to prepare IMCs and explores their structural properties. Subsequently, catalytic applications of the IMCs are introduced, focusing on the key reactions and highlighting their superior catalytic performance compared to conventional catalysts. Future perspectives for, and challenges to, the catalysis of IMCs are then proposed. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis: From Nano- and Cluster-Catalysts to Single-Atom Catalysts)

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10 pages, 2068 KiB

Open AccessArticle

Catalytic Effect of Alkali Metal Ions on the Generation of CO and CO₂ during Lignin Pyrolysis: A Theoretical Study

by Xiaoyan Jiang, Yiming Han, Baojiang Li, Ji Liu, Guanzheng Zhou, Xiaojiao Du, Shougang Wei, Hanxian Meng and Bin Hu

Catalysts 2024, 14(8), 537; https://doi.org/10.3390/catal14080537 - 18 Aug 2024

Viewed by 489

Abstract

A density functional theory method was employed to conduct theoretical calculations on the pyrolysis reaction pathways of lignin monomer model compounds with an aldehyde or carboxyl group under the catalytic effect of alkali metal ions Na⁺ and K⁺, exploring their [...] Read more.

A density functional theory method was employed to conduct theoretical calculations on the pyrolysis reaction pathways of lignin monomer model compounds with an aldehyde or carboxyl group under the catalytic effect of alkali metal ions Na⁺ and K⁺, exploring their influence on the formation of the small molecular gaseous products CO and CO₂. The results indicate that Na⁺ and K⁺ can easily bind with the oxygen-containing functional groups of the lignin monomer model compounds to form stable and low-energy complexes. Except for benzaldehyde and p-hydroxybenzaldehyde, Na⁺ and K⁺ can facilitate the decarbonylation reactions of other benzaldehyde-based and phenylacetaldehyde-based lignin monomer model compounds during the pyrolysis process, thereby enhancing the generation of CO. When the characteristic functional groups on the benzene rings of benzaldehyde-based and phenylacetaldehyde-based lignin monomer model compounds are the same, the phenylacetaldehyde-based ones are more prone to undergo decarbonylation than the benzaldehyde-based ones. Additionally, both Na⁺ and K⁺ can inhibit the decarboxylation reactions of benzoic acid-based and phenylacetic acid-based lignin monomer model compounds, thereby restraining the formation of CO₂. When the characteristic functional groups on the benzene rings of benzoic acid-based and phenylacetic acid-based lignin monomer model compounds are the same, the phenylacetic acid-based ones are more difficult to undergo decarboxylation than the benzoic acid-based ones. Full article

(This article belongs to the Collection Catalytic Conversion of Biomass to Bioenergy)

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18 pages, 4714 KiB

Open AccessFeature PaperArticle

α-L-Arabinofuranosidases of Glycoside Hydrolase Families 43, 51 and 62: Differences in Enzyme Substrate and Positional Specificity between and within the GH Families

by Walid Fathallah and Vladimír Puchart

Catalysts 2024, 14(8), 536; https://doi.org/10.3390/catal14080536 - 17 Aug 2024

Viewed by 423

Abstract

The increasing number of uncharacterized proteins in the CAZy database highlights the importance of their functional characterization. Therefore, the substrate and positional specificity of 34 α-L-arabinofuranosidases classified into GH43, GH51, and GH62 families was determined on arabinoxylan, arabinan, and derived oligosaccharides (many enzyme–substrate [...] Read more.

The increasing number of uncharacterized proteins in the CAZy database highlights the importance of their functional characterization. Therefore, the substrate and positional specificity of 34 α-L-arabinofuranosidases classified into GH43, GH51, and GH62 families was determined on arabinoxylan, arabinan, and derived oligosaccharides (many enzyme–substrate combinations were examined for the first time) covering all possible kinds of arabinofuranosyl branches using TLC. Arabinoxylan was efficiently debranched by the majority of the tested proteins. Most of them showed AXH-m specificity, acting on 2- or 3-monoarabinosylated substrates, while AXH-d3 specificity (liberation of 3-linked arabinose solely from 2,3 doubly decorated substrates) was found mainly in the subfamily GH43_10, harbouring enzymes of both types. Several GH51 enzymes, however, released arabinose also from a xylooligosaccharide doubly arabinosylated at the non-reducing end. The AXH-m and AXH-d3 specificities correlated well with the dearabinosylation of arabinan and arabinooligosaccharides, which were debranched by all GH51 representatives and some GH43 and GH62 members. The GH51 and GH62 arabinan-debranching enzymes also hydrolyzed debranched arabinan, while within the GH43 family the linear arabinan-degrading ability was found only in the GH43_26 subfamily, comprising specific exo 1,5-α-L-arabinofuranosidases. This study demonstrates a first attempt in the systematic examination of a relationship between CAZy classification and substrate and positional specificities of various α-L-arabinofuranosidases. Full article

(This article belongs to the Section Biocatalysis)

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Full article ">Figure 1
TLC analysis of wheat arabinoxylan (WAX) hydrolysates. A schematic structure of the polysaccharide in non-abbreviated and abbreviated forms is shown above the TLC plate. The plate was developed in the solvent system of 1-butanol/ethanol/water (10:8:5, by vol.; system 1), and the sugars were visualized using orcinol detection reagent. The GH43, GH51, and GH62 enzymes are marked in black, blue, and green colours, respectively. Aliquots of the reaction mixtures were spotted after 1 and/or 4 days of incubation. Full article ">Figure 2
TLC analysis of hydrolysates of branched arabinoxylooligosaccharide mixture comprising 33-α-L-arabinofuranosyl-xylotetraose (XA3XX) and 23-α-L-arabinofuranosyl-xylotetraose (XA2XX). The plate was developed twice in the solvent system of 1-propanol/ethanol/water (7:1:2, by vol.; system 3), and the sugars were visualized using orcinol detection reagent. The GH43, GH51, and GH62 enzymes are marked in black, blue, and green colours, respectively. Aliquots of the reaction mixtures were spotted after 4 h, 1, and/or 4 days of incubation. Full article ">Figure 3
Comparison of amino acid sequences of the proteins used in this study classified into GH43 family. Enzymes belonging to subfamilies that are represented by multiple members used in this work were only chosen for this comparison. Panel (A): multiple sequence alignment of the sequences. The enzymes with solved 3-D structures are marked with a $ symbol (accessible under PDB codes 5A8C and 3QEF for BtAbf43B and CjAbf43A). The asterisk at the end of the BtAbf43D sequence denotes C-terminus of the protein. Catalytically competent amino acids, i.e., catalytic base, catalytic acid, and modulator of catalytic acid, are marked in violet, green, and cyan, respectively. The residues forming subsites −1 and +1 are highlighted in yellow and red, respectively. The residues interacting with the substrate in other subsites are indicated in grey. Panel (B): phylogenetic tree corresponding to the multiple sequence alignment. Classification of the enzymes into the GH43 subfamilies is indicated. Full article ">Figure 4
TLC analysis of sugar beet arabinan (SBA) hydrolysates. Schematic structure of the polysaccharide in non-abbreviated and abbreviated forms is shown above the TLC plate. The plate was developed in the solvent system of 1-butanol/ethanol/water (10:8:5, by vol.; system 1), and the sugars were visualized using orcinol detection reagent. The GH43, GH51, and GH62 enzymes are marked in black, blue, and green colours, respectively. Aliquots of the reaction mixtures were spotted after 1 and/or 4 days of incubation. Full article ">Figure 5
TLC analysis of hydrolysates of branched arabinooligosaccharide mixture comprising 22,32-di-α-L-arabinofuranosyl-(1,5)-α-L-arabinotriose (AA2,3A) and 32-α-L-arabinofuranosyl-(1,5)-α-L-arabinotetraose (AAA3A). The plate was developed twice in the solvent system of chloroform/acetic acid/water (6:7:1, by vol.; system 2), and the sugars were visualized using orcinol detection reagent. The GH43, GH51. and GH62 enzymes are marked in black, blue. and green colours, respectively. Aliquots of the reaction mixtures were spotted after 4 h, 1, and/or 4 days of incubation. Full article ">Figure 6
TLC analysis of debranched arabinan (DA) hydrolysates. The schematic structure of the polysaccharide is shown above the TLC plate. The plate was developed in the solvent system of 1-butanol/ethanol/water (10:8:5, by vol.; system 1), and the sugars were visualized using orcinol detection reagent. The GH43, GH51, and GH62 enzymes are marked in black, blue, and green colours, respectively. Aliquots of the reaction mixtures were spotted after 2 h, 1, and/or 4 days of incubation. Full article ">

15 pages, 2562 KiB

Open AccessArticle

Sludge Recycling from Non-Lime Purification of Electrolysis Wastewater: Bridge from Contaminant Removal to Waste-Derived NO_X SCR Catalyst

by Ju Gao, Fucheng Sun, Pei Liu, Jizhi Zhou and Yufeng Zhang

Catalysts 2024, 14(8), 535; https://doi.org/10.3390/catal14080535 - 17 Aug 2024

Viewed by 661

Abstract

Catalysts for the selective catalytic reduction (NO_X SCR) of nitrogen oxides can be obtained from sludge in industrial waste treatment, and, due to the complex composition of sludge, NO_X SCR shows various SCR efficiencies. In the current work, an SCR catalyst [...] Read more.

Catalysts for the selective catalytic reduction (NO_X SCR) of nitrogen oxides can be obtained from sludge in industrial waste treatment, and, due to the complex composition of sludge, NO_X SCR shows various SCR efficiencies. In the current work, an SCR catalyst developed from the sludge produced with Fe/C micro-electrolysis Fenton technology (MEF) in wastewater treatment was investigated, taking into account various sludge compositions, Fe/C ratios, and contaminant contents. It was found that, at about 300 °C, the NO_X removal rate could reach 100% and there was a wide decomposition temperature zone. The effect of individual components of electroplating sludge, i.e., P, Fe and Ni, on NO_X degradation performance of the obtained solids was investigated. It was found that the best effect was achieved when the Fe/P was 8/3 wt%, and variations in the Ni content had a limited effect on the NO_X degradation performance. When the Fe/C was 1:2 and the Fe/C/P was 1:2:0.4, the electroplating sludge formed after treatment with Fe/C MEF provided the best NO_X removal rate at 100%. Moreover, the characterization results show that the activated carbon was also involved in the catalytic reduction degradation of NO_X. An excessive Fe content may cause agglomeration on the catalyst surface and thus affect the catalytic efficiency. The addition of P effectively reduces the catalytic reaction temperature, and the formation of phosphate promotes the generation of adsorbed oxygen, which in turn contributes to improvements in catalytic efficiency. Therefore, our work suggests that controlling the composition in the sludge is an efficient way to modulate SCR catalysis, providing a bridge from contaminant-bearing waste to efficient catalyst. Full article

(This article belongs to the Special Issue Homogeneous and Heterogeneous Catalytic Oxidation and Reduction)

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Fe/C + H2O2 treatment of electroplating wastewater effluent in (a) TP, Ni, and Fe2+ and (b) pH change. Full article ">Figure 2
The effect of composition on NOX removal efficiency. Full article ">Figure 3
The effects of (a) P, (b) Ni, and (c) Fe on NOX removal efficiency. Full article ">Figure 4
The effects of (a) Fe/C and (b) P concentration in the pollutants on NOX removal efficiency. Full article ">Figure 5
SEM images of (a) Fe8/P4/Ni/C (10.0 μm); (b) Fe8/P4/Ni/C (1.0 μm); (c) Fe10/P5/Ni/C (10.0 μm); and (d) Fe10/P5/Ni/C samples (1.0 μm). Full article ">Figure 6
(a) The NH3 TPD curves of Fe, Fe/Ni and Fe/Ni/P/C; (b) the NH3 TPD curves of Fe/Ni/P/C samples with different P contents; and (c) the NO2 TPD curves of the sample before and after reaction. Full article ">Figure 7
Schematic of the reaction. Full article ">Figure 8
The NOX catalytic experimental device and technological process. Full article ">

12 pages, 3975 KiB

Open AccessArticle

Facile Synthesis of Ni(OH)₂ through Low-Temperature N-Doping for Efficient Hydrogen Evolution

by Zi-Zhang Liu, Ruo-Yao Fan, Ning Yu, Ya-Nan Zhou, Xin-Yu Zhang, Bin Dong and Zi-Feng Yan

Catalysts 2024, 14(8), 534; https://doi.org/10.3390/catal14080534 - 16 Aug 2024

Viewed by 390

Abstract

Nickel hydroxide is a potentially cheap non-precious metal catalytic material for alkaline hydrogen evolution reactions (HERs). Herein, a nickel form (NF)-based nitrogen-modified nickel hydroxide (N-Ni(OH)₂/NF) with interlaced two-dimensional (2D) nanosheet structures was synthesized by a simple one-step ammonia vapor-phase hydrothermal method [...] Read more.

Nickel hydroxide is a potentially cheap non-precious metal catalytic material for alkaline hydrogen evolution reactions (HERs). Herein, a nickel form (NF)-based nitrogen-modified nickel hydroxide (N-Ni(OH)₂/NF) with interlaced two-dimensional (2D) nanosheet structures was synthesized by a simple one-step ammonia vapor-phase hydrothermal method for efficient electrocatalytic HERs. The effect of the reaction temperature of the catalyst preparation on the HERs’ performance was studied in detail. The HER activity of N-Ni(OH)₂/NF is enhanced by the large specific surface area, mass transfer and electron conductivity provided by a unique and suitable 2D nanostructure and nitrogen doping. The obtained N-Ni(OH)₂/NF not only shows a superior HERs performance, but also exhibits good stability during long-term electrolysis. Full article

(This article belongs to the Special Issue Non-novel Metal Electrocatalytic Materials for Clean Energy)

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Schematic illustration of one-step access to N-Ni(OH)2/NF. Full article ">Figure 2
XRD patterns of N90-Ni(OH)2/NF, N130-Ni(OH)2/NF and N180-Ni(OH)2/NF. Full article ">Figure 3
XPS spectra of N130-Ni(OH)2/NF: (a) survey; (b) N 1s; (c) Ni 2p. Full article ">Figure 4
SEM images of (a,b) N90-Ni(OH)2/NF; (c,d) N130-Ni(OH)2/NF and (e,f) N180-Ni(OH)2/NF. Full article ">Figure 5
(a) TEM and (b) HRTEM images of N130-Ni(OH)2/NF and (c) corresponding element mapping images. Full article ">Figure 6
Electrocatalytic measurements for HER at 1.0 M KOH. (a) Linear sweep voltammogram (LSV). (b) Tafel plots. (c) Electrochemical impedance spectroscopy (EIS). (d) Determined double-layer capacitance (Cdl). Full article ">Figure 7
The Faraday efficiency for HER on N130-Ni(OH)2/NF in 1 M KOH. Full article ">Figure 8
Stability test of N130-Ni(OH)2/NF. (a) LSV before and after cyclic voltammograms (CVs) for 5000 cycles. (b) 12 h CA test. Full article ">

18 pages, 4266 KiB

Open AccessArticle

Selective Oligomerization of Isobutylene in Mixed C4 with Co/BETA-Loaded Molecular Sieve Catalysts

by Xiaoping Chen, Panhu Yu, Hui Tian and Shuguang Xiang

Catalysts 2024, 14(8), 533; https://doi.org/10.3390/catal14080533 - 16 Aug 2024

Viewed by 366

Abstract

This paper investigates the use of loaded Co/BETA molecular sieve catalysts for the selective oligomerization of isobutylene. The physicochemical properties of Co/BETA molecular sieves were characterized using XRD, BET, NH3-TPD, FT-IR, XPS, and Py-FTIR. The effects of different active component loadings, reaction temperatures, [...] Read more.

This paper investigates the use of loaded Co/BETA molecular sieve catalysts for the selective oligomerization of isobutylene. The physicochemical properties of Co/BETA molecular sieves were characterized using XRD, BET, NH3-TPD, FT-IR, XPS, and Py-FTIR. The effects of different active component loadings, reaction temperatures, and reaction air velocities on the selective oligomerization of isobutylene were investigated in a fixed-bed reactor. The results showed that the catalytic effect was optimal when the Co loading was 6%, the reaction temperature was 60 °C, the reaction pressure was 1 MPa, and the reaction air speed was 1 h⁻¹. The isobutylene conversion was greater than 74%, the C₈⁼ selectivity was approximately 70%, and the C₈⁼ yield reached 51.69% with minimal loss of n-butene, providing good catalytic capacity and efficiency. Full article

(This article belongs to the Section Catalytic Materials)

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18 pages, 10151 KiB

Open AccessFeature PaperArticle

Application of Different Waveforms of Pulsed Current in the Classical Electro-Cocatalytic Process for Effective Removal of Sulfamethoxazole: Oxidation Mechanisms

by Jingkai Fang, Yongjian Wang, Jiahao Wang, Igor Ying Zhang and Rongfu Huang

Catalysts 2024, 14(8), 532; https://doi.org/10.3390/catal14080532 - 16 Aug 2024

Viewed by 548

Abstract

In this study, sulfamethoxazole (SMX) was applied as the model pollutant to assess the performance of pulsed current (PC) waveforms in the decontamination efficiency of the PC/peroxymonosulfate (PMS)/Fe(III) process and to investigate underlying oxidation mechanisms. Among the various waveforms tested, the sinusoidal wave [...] Read more.

In this study, sulfamethoxazole (SMX) was applied as the model pollutant to assess the performance of pulsed current (PC) waveforms in the decontamination efficiency of the PC/peroxymonosulfate (PMS)/Fe(III) process and to investigate underlying oxidation mechanisms. Among the various waveforms tested, the sinusoidal wave (SIN), combined with the Dimensionally Stable Anode (DSA) electrode, demonstrated superior degradation performance, with the order being SIN > ramp > square > direct current (DC). The operational conditions for the SIN/PMS/Fe(III) system were optimized to an initial pH of 3, a voltage of 6 V, 0.6 mmol/L of Fe³⁺, 1.0 mmol/L of PMS, and a frequency of 1 kHz. The results of quenching and probe experiments confirmed the generation of abundant reactive radicals such as ^•OH, SO₄^•−, O₂^•−, Fe(IV), and ¹O₂ in the SIN/PMS/Fe(III) process, which collectively enhanced the degradation of SMX. Additionally, results of high-resolution mass spectrometry analysis were employed to identify the SMX oxidation byproducts, and the toxicity of SMX byproducts was evaluated. Overall, the SIN/PMS/Fe(III) process exhibits effective degradation capacity with high energy efficiency, establishing itself as an effective strategy for the practical treatment of medical wastewater. Full article

(This article belongs to the Section Industrial Catalysis)

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18 pages, 3108 KiB

Open AccessFeature PaperReview

The Advancement of Supported Bimetallic Catalysts for the Elimination of Chlorinated Volatile Organic Compounds

by Hongxia Lin, Yuxi Liu, Jiguang Deng, Lin Jing, Zhiwei Wang, Lu Wei, Zhen Wei, Zhiquan Hou, Jinxiong Tao and Hongxing Dai

Catalysts 2024, 14(8), 531; https://doi.org/10.3390/catal14080531 - 16 Aug 2024

Viewed by 496

Abstract

Chlorinated volatile organic compounds (CVOCs) are persistent pollutants and harmful to the atmosphere, environment, and human health. The catalytic elimination of CVOCs has become a hotspot of interest due to their self-toxicity, the secondary generation of chlorinated by-products, and the Cl poisoning of [...] Read more.

Chlorinated volatile organic compounds (CVOCs) are persistent pollutants and harmful to the atmosphere, environment, and human health. The catalytic elimination of CVOCs has become a hotspot of interest due to their self-toxicity, the secondary generation of chlorinated by-products, and the Cl poisoning of catalysts. The development of high-performance, highly selective, and anti-poisoning catalysts is a critical issue. Bimetallic catalysts exhibit an improved dechlorination performance, poisoning resistance, and product selectivity through the modulation of geometrical and electronic structures. The present review article gives a brief overview of the recent advancements in the preparation of bimetallic catalysts and their catalytic CVOC elimination activities. In addition, representative case studies are provided to investigate the physicochemical properties, CVOC conversion, CO_x and inorganic chlorine species selectivities, and by-product control so that the structure–performance relationships of bimetallic catalysts can be established. Furthermore, this review article provides a fundamental understanding of designing bimetallic catalysts with specific active components and the desired physicochemical properties for target reactions. In the end, related perspectives for future work are proposed. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis: From Nano- and Cluster-Catalysts to Single-Atom Catalysts)

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15 pages, 4943 KiB

Open AccessFeature PaperArticle

Dual-Function Photocatalysis in the Visible Spectrum: Ag-G-TiO₂ for Simultaneous Dye Wastewater Degradation and Hydrogen Production

by Tarek Ahasan, Pei Xu and Huiyao Wang

Catalysts 2024, 14(8), 530; https://doi.org/10.3390/catal14080530 - 15 Aug 2024

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Abstract

Photocatalytic processes offer promising solutions for environmental remediation and clean energy production, yet their efficiency under the visible light spectrum remains a significant challenge. Here, we report a novel silver–graphene (Ag-G) modified TiO₂ (Ag-G-TiO₂) nanocomposite photocatalyst that demonstrates remarkably enhanced [...] Read more.

Photocatalytic processes offer promising solutions for environmental remediation and clean energy production, yet their efficiency under the visible light spectrum remains a significant challenge. Here, we report a novel silver–graphene (Ag-G) modified TiO₂ (Ag-G-TiO₂) nanocomposite photocatalyst that demonstrates remarkably enhanced photocatalytic activity for both dye wastewater degradation and hydrogen production under visible and UV light irradiation. Through comprehensive characterization and performance analysis, we reveal that the Ag-G modification narrows the TiO₂ bandgap from 3.12 eV to 1.79 eV, enabling efficient visible light absorption. The nanocomposite achieves a peak hydrogen production rate of 191 μmolesg⁻¹h⁻¹ in deionized (DI) water dye solution under visible light, significantly outperforming unmodified TiO₂. Intriguingly, we observe an inverse relationship between dye degradation efficiency and hydrogen production rates in dye solutions with tap water versus DI water, highlighting the critical role of water composition in photocatalytic processes. This work not only advances the understanding of fundamental photocatalytic mechanisms but also presents a promising photocatalyst for solar-driven environmental remediation and clean energy production. The Ag-G-TiO₂ nanocomposite’s enhanced performance across both visible and UV spectra, coupled with its dual functionality in dye degradation and hydrogen evolution, represents a significant step towards addressing critical challenges in water treatment and sustainable energy generation. Our findings highlight the complex interplay between light absorption and reaction conditions, offering new insights for optimizing photocatalytic systems. This research paves the way for developing more efficient and versatile photocatalysts, potentially contributing to the global transition towards sustainable technologies and circular economy in waste management and energy production. Full article

(This article belongs to the Special Issue Advances in Photocatalytic Wastewater Purification, 2nd Edition)

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31 pages, 9696 KiB

Open AccessArticle

Production of Green Fuel Using a New Synthetic Magnetite Mesoporous Nano-Silica Composite Catalyst for Oxidative Desulfurization: Experiments and Process Modeling

by Aysar T. Jarullah, Ahmed K. Hussein, Ban A. Al-Tabbakh, Shymaa A. Hameed, Iqbal M. Mujtaba, Liqaa I. Saeed and Jasim I. Humadi

Catalysts 2024, 14(8), 529; https://doi.org/10.3390/catal14080529 - 15 Aug 2024

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Abstract

Producing an eco-friendly fuel with the least amount of sulfur compounds has been an ongoing issue for petroleum refineries. In this study, bentonite (which is a cheap material and is locally available in abundance) is employed to prepare a nano-silica catalyst with a [...] Read more.

Producing an eco-friendly fuel with the least amount of sulfur compounds has been an ongoing issue for petroleum refineries. In this study, bentonite (which is a cheap material and is locally available in abundance) is employed to prepare a nano-silica catalyst with a high surface area to be used for the oxidative desulfurization of kerosene. Two composite catalysts of Fe/silica were supported on CAT-1 (0% HY-zeolite and 100% nano-silica) and CAT-2 (20% HY-zeolite and 80% nano-silica). The activity of the catalysts was evaluated in a batch ODS (oxidative desulfurization) process at temperatures of 30, 60, 90, and 120 °C, a pressure of 1 atm, and a reaction time of 30, 60, 90, and 120 min using 120 L/h of air as the oxidant. The results revealed that the highest total sulfur removal efficiency was 50% and 87.88% for 100% nano-silica (CAT-1) and 80% nano-silica (CAT-2), respectively. The experimental data were then used to construct and validate an accurate mathematical model of the process. The operational parameters for eliminating more than 99% of sulfur and producing eco-friendly fuel were then achieved by using the model. The testing methods for these characterizing materials included X-ray diffraction (XRD), thermal gravimetric examination (TGA), X-ray fluorescence (XRF), and surface area (BET). The outcomes indicated that the addition of HY-zeolite increased the activity of the catalyst (CAT-2 > CAT-1). Full article

(This article belongs to the Special Issue Designing Catalytic Desulfurization Processes to Prepare Clean Fuels, 2nd Edition)

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12 pages, 5341 KiB

Open AccessArticle

Defective TiO₂/MIL-88B(Fe) Photocatalyst for Tetracycline Degradation: Characterization and Augmented Photocatalytic Efficiency

by Dongsheng Xiang, Zhihao Wang, Jingwen Xu, Hongdan Shen, Xiaodong Zhang and Ning Liu

Catalysts 2024, 14(8), 528; https://doi.org/10.3390/catal14080528 - 15 Aug 2024

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Abstract

Photocatalysts, such as TiO₂, are widely used in photoreduction. However, drawbacks like their wide band gap and short carrier lifetime lead to lower efficiencies with their use. Introducing defects and forming heterostructures of TiO₂ could extend the carrier’s light-harvesting range [...] Read more.

Photocatalysts, such as TiO₂, are widely used in photoreduction. However, drawbacks like their wide band gap and short carrier lifetime lead to lower efficiencies with their use. Introducing defects and forming heterostructures of TiO₂ could extend the carrier’s light-harvesting range from UV to visible light and enhance its lifetime. Herein, an electron-beam irradiation-defected TiO₂ was induced in MIL-88B(Fe). The structure of the material was characterized using XRD, FT-IR, TEM, HRTEM, and XPS techniques. Remarkably, TiO₂ under 300 kGy electron-beam irradiation performed the best with a series of 0, 100, 300, and 500 kGy irradiation ratios. PL and UV–vis DRS were utilized to measure the material’s optical properties. The introduction of MIL-88B(Fe) expanded the light response range, reduced the optical band gap, and lengthened the carrier lifetime of the defective TiO₂ composite photocatalysts, resulting in superior TC photoreduction capabilities of 88B5%300, which degraded 97% of tetracycline (10 mg/L) in water after 120 min. Full article

(This article belongs to the Special Issue Green Chemistry and Catalysis)

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13 pages, 4063 KiB

Open AccessArticle

A Highly Efficient Tribocatalysis of La/ZnO Powders for Degradation of Rhodamine B

by Dobrina K. Ivanova, Bozhidar I. Stefanov and Nina V. Kaneva

Catalysts 2024, 14(8), 527; https://doi.org/10.3390/catal14080527 - 15 Aug 2024

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Abstract

Tribocatalysis is a promising environmental remediation technique that utilizes the triboelectric effect, produced when dissimilar materials interact through friction, to generate charges promoting catalytic reactions. In this work, the tribocatalytic degradation of an organic dye—Rhodamine B (RhB)—has been experimentally realized using pure and [...] Read more.

Tribocatalysis is a promising environmental remediation technique that utilizes the triboelectric effect, produced when dissimilar materials interact through friction, to generate charges promoting catalytic reactions. In this work, the tribocatalytic degradation of an organic dye—Rhodamine B (RhB)—has been experimentally realized using pure and 2 mol.% La-modified/ZnO powders, synthesized via a simple hydrothermal method. The effects of annealing on the tribocatalytic activity of the La/ZnO catalysts are also studied at 100 and 500 °C. The La/ZnO-modified catalysts showed an enhanced RhB degradation efficiency with 92% removal within 24 h, compared to only 58% for the pure ZnO. The effects of annealing were found to be detrimental, with RhB removal efficiencies dropping from 92 to 69% in the 100–500 °C range. The catalysts’ cycling stability was found to be excellent within three cycles. Ultimately, it is demonstrated that by utilizing La/ZnO powders, contaminated wastewater can be efficiently treated through employing tribocatalysis. Full article

(This article belongs to the Section Catalytic Materials)

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24 pages, 5842 KiB

Open AccessArticle

Porous Nanostructured Catalysts Based on Silicates and Their Surface Functionality: Effects of Silica Source and Metal Added in Glycerol Valorization

by José Vitor C. Carmo, Joabson Nogueira, Gabriela M. Bertoldo, Francisco E. Clemente, Alcineia C. Oliveira, Adriana F. Campos, Gian C. S. Duarte, Samuel Tehuacanero-Cuapa, José Jiménez-Jiménez and Enrique Rodríguez-Castellón

Catalysts 2024, 14(8), 526; https://doi.org/10.3390/catal14080526 - 15 Aug 2024

Viewed by 452

Abstract

A series of nanospherical-shaped silicates containing heteroatoms (Al, Zr or Ti) were successfully synthesized using tetraethylorthosilicate (TEOS) or silica colloids as a silicon source. These metallosilicate nanospheres were used as silicon nutrients to obtain silicalite zeolites with micro-mesoporosity and improved textural properties. The [...] Read more.

A series of nanospherical-shaped silicates containing heteroatoms (Al, Zr or Ti) were successfully synthesized using tetraethylorthosilicate (TEOS) or silica colloids as a silicon source. These metallosilicate nanospheres were used as silicon nutrients to obtain silicalite zeolites with micro-mesoporosity and improved textural properties. The results demonstrated that TEOS acted as a suitable silicon source to produce amorphous silicates and a spherical-type zeolite architecture with Zr and Ti heteroatoms included in their framework, with preferable particle size and crystallinity. The surface functionality of the mesostructured nanospheres and zeolite silicates provide active centers for the esterification of glycerol with acetic acid (EG) reaction. The dispersion of Cu entities on the surface of the zeolites achieved high glycerol conversions selectively producing triacetin in comparison with Fe counterparts. Full article

(This article belongs to the Special Issue Novel Nanocatalysts for Sustainable and Green Chemistry)

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20 pages, 4448 KiB

Open AccessArticle

Biogenic Synthesis Based on Cuprous Oxide Nanoparticles Using Eucalyptus globulus Extracts and Its Effectiveness for Removal of Recalcitrant Compounds

by Pablo Salgado, Katherine Márquez and Gladys Vidal

Catalysts 2024, 14(8), 525; https://doi.org/10.3390/catal14080525 - 14 Aug 2024

Viewed by 603

Abstract

Recalcitrant compounds resulting from anthropogenic activity are a significant environmental challenge, necessitating the development of advanced oxidation processes (AOPs) for effective remediation. This study explores the synthesis of cuprous oxide nanoparticles on cellulose-based paper (Cu₂O@CBP) using Eucalyptus globulus leaf extracts, leveraging [...] Read more.

Recalcitrant compounds resulting from anthropogenic activity are a significant environmental challenge, necessitating the development of advanced oxidation processes (AOPs) for effective remediation. This study explores the synthesis of cuprous oxide nanoparticles on cellulose-based paper (Cu₂O@CBP) using Eucalyptus globulus leaf extracts, leveraging green synthesis techniques. The scanning electron microscopy (SEM) analysis found the average particle size 64.90 ± 16.76 nm, X-ray diffraction (XRD) and Raman spectroscopy confirm the Cu₂O structure in nanoparticles; Fourier-transform infrared spectroscopy (FTIR) suggests the reducing role of phenolic compounds; and ultraviolet–visible diffuse reflectance spectroscopy (UV-Vis DRS) allowed us to determine the band gap (2.73 eV), the energies of the valence band (2.19 eV), and the conduction band (−0.54 eV) of Cu₂O@CBP. The synthesized Cu₂O catalysts demonstrated efficient degradation of methylene blue (MB) used as a model as recalcitrant compounds under LED-driven visible light photocatalysis and heterogeneous Fenton-like reactions with hydrogen peroxide (H₂O₂) using the degradation percentage and the first-order apparent degradation rate constant (k_app). The degradation efficiency of MB was pH-dependent, with neutral pH favoring photocatalysis (k_app = 0.00718 min⁻¹) due to enhanced hydroxyl (·OH) and superoxide radical (O₂·⁻) production, while acidic pH conditions improved Fenton-like reaction efficiency (k_app = 0.00812 min⁻¹) via ·OH. The reusability of the photocatalysts was also evaluated, showing a decline in performance for Fenton-like reactions at acidic pH about 22.76% after five cycles, while for photocatalysis at neutral pH decline about 11.44% after five cycles. This research provides valuable insights into the catalytic mechanisms and supports the potential of eco-friendly Cu₂O nanoparticles for sustainable wastewater treatment applications. Full article

(This article belongs to the Section Photocatalysis)

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4 pages, 171 KiB

Open AccessEditorial

Special Issue Catalysis for Bitumen/Heavy Oil Upgrading and Petroleum Refining

by Irek I. Mukhamatdinov and Nikita N. Sviridenko

Catalysts 2024, 14(8), 524; https://doi.org/10.3390/catal14080524 - 13 Aug 2024

Viewed by 500

Abstract

Currently, fossil fuels continue to play a crucial role in daily life [...] Full article

(This article belongs to the Special Issue Catalysis for Bitumen/Heavy Oil Upgrading and Petroleum Refining)

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Catalysts, Volume 14, Issue 8 (August 2024) – 85 articles

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