ABSTRACT SiC nanowires have been rarely investigated or explored along their axial direction by t... more ABSTRACT SiC nanowires have been rarely investigated or explored along their axial direction by transmission electron microscopy (TEM). Here we report the investigation of the cross-section microstructure of SiC nanowires by embedding them into Al matrix. Morphology of SiC nanowires was cylindrical with smooth surface or bamboo shape. Cubic (3C-SiC) and hexagonal structure (2H-SiC) phases were detected by X-ray diffraction (XRD) analysis. High density stacking faults were observed in both the cylindrical and bamboo shaped nanowires which were perpendicular to their axial direction. Selected area electron diffraction (SAED) patterns of the cylindrical and bamboo shaped SiC nanowires both in the perpendicular and parallel direction to the axial direction were equivalent in the structure. After calculation and remodeling, it has been found that the SAED patterns were composed of two sets of diffraction patterns, corresponding to 2H-SiC and 3C-SiC, respectively. Therefore, it could be concluded that the SiC nanowires are composed of a large number of small fragments that are formed by hybrid 3C-SiC and 2H-SiC structures.
ABSTRACT Al matrix composites reinforced with one-dimensional nano-materials (for instance nanotu... more ABSTRACT Al matrix composites reinforced with one-dimensional nano-materials (for instance nanotubes, nanowires and nanofibres) have been widely investigated in the past decade. However, the preparation, microstructure and mechanical behavior of high content (>10 vol%) SiC nanowires reinforced Al (SiCnw/Al) has not been reported yet. In the present work, 15 vol% SiCnw/6061Al composite was prepared by the pressure infiltration method. SiCnw/6061Al composite demonstrated good machining performance since continuous chip was obtained after cut by carbide turning tools. SiC nanowires were uniformly distributed without any observance of SiC agglomerates. Long SiC nanowires were observed after etching, implying that the preparation process had shown minor damage to the SiC nanowires and therefore, the pressure infiltration method is a feasible and successful way to prepare high content SiCnw/Al composites. The interface between SiC nanowires and Al was well bonded, and no significant interfacial product was found. After aging treatment, 15 vol% SiCnw/6061Al composite demonstrated high strength (over 1000 MPa), while a comparable plasticity as Al matrix was retained. The strengthening effect of SiC nanowires could be fully utilized through the fracture of SiC nanowires. Moreover, the grain size of Al matrix in SiCnw/6061Al composite was significantly refined and polycrystalline diffraction rings were observed. Therefore, supplemented to previous results in one-dimensional nano-materials reinforced Al matrix composites, fine-grain was also found as another main strengthening mechanism.
A set of Rh-containing catalysts (Rh-MCM-41, Rh-SBA-15, Rh-KIT-6 and Rh-MCF, nominal Rh content =... more A set of Rh-containing catalysts (Rh-MCM-41, Rh-SBA-15, Rh-KIT-6 and Rh-MCF, nominal Rh content = 1 wt.%) has been prepared by wet impregnation of mesoporous silicas and tested for high concentration N2O abatement. The physico-chemical properties of the materials have been investigated by means of complementary techniques.
The best performances, in terms of N2O decomposition, have been achieved for the Rh-MCF catalyst, due to the better textural properties of the MCF silica. In fact, the MCF-type support exhibits three-dimensional mesoporosity with ultra-large cells (up to 40 nm), which allow a uniform distribution of small RhOx particles (≈1 nm) over the high (internal) surface area of the MCF. Moreover, the Rh active sites are also readily accessible to N2O molecules.
The most promising catalyst has shown the highest amount of Rh1+ species, the easiest rhodium reducibility and the greatest abundance of Rh surface sites. These important features reflect the different Rh particle sizes and play a role in catalytic activity.
A remarkable relationship between the catalytic activity and the dimension of the RhOx particles has been observed in the 1–2.5 nm size domain, thus confirming the dispersion-sensitivity of N2O decomposition over RhOx nanoparticles.
Nanostructured TiO2/KIT-6 catalysts with different concentrations of incorporated TiO2, have been... more Nanostructured TiO2/KIT-6 catalysts with different concentrations of incorporated TiO2, have been synthesized, characterized, and examined in order to improve the photocatalytic reduction of carbon dioxide (CO2) feedstock with water vapor (H2O) to produce tunable value-added energy products. Nanostructured TiO2, dispersed on KIT-6 (three-dimensional mesoporous silica), was found to be present in both the silica framework and on the surface, where it produced large surface area photocatalysts with enhanced adsorption capability of the reactants to photocatalytically convert into CH4, CH3OH (hydrocarbons) and CO, H2 (similar to syngas). The formed products were influenced directly by the dispersed TiO2 concentration as well as by the calcination temperature. Hydrocarbon and CO formation as well as the reaction kinetics improved as the TiO2 concentration was increased from 1 to 20 wt%. However, a further increase in TiO2 loadings (to 90%) decreased the hydrocarbon and CO, and increased H2 formation. The highest optimization toward hydrocabon selectivity was shown by 20 wt% TiO2, while a 90 wt% TiO2 loading was more selective for H2 formation. This was likely due to the uniform dispersion and stabilization of the anatase TiO2 with 20 wt% on KIT-6, which in turn allowed more CO2 adsorption and a better light penetration than 90% TiO2/KIT-6 in which it showed a bulk phase and large agglomerates with light penetration limitations that were more favorable for H2O adsorption. A reaction mechanism, which has helped to understand these findings, has been proposed. Moreover, a 24 h activity test with the optimized 20 wt% TiO2/KIT-6 showed an increase in the product yield but only a minor, gradual decrease in the reaction rate, which points out that these photocatalysts could be promising for turning CO2 greenhouse gas feedstock into selective renewable energy products.
Matrix alloying is an effective and convenient method to improve the interface bonding strength f... more Matrix alloying is an effective and convenient method to improve the interface bonding strength for continuous carbon fiber reinforced magnesium matrix composites. In this work, rare earth metal Gd was selected as an alloying element to improve the interface bonding of Cf/Mg composite. Cf/Mg composites with different Gd content were fabricated by pressure infiltration method. The effect of Gd addition on the interfacial microstructures and mechanical properties of the composites were investigated. The results showed that the rare earth Gd tended to segregate at interface area to form Gd2O3 layer and particle phase Mg7Gd. Both the interfacial products enhanced the interface bonding strength which can be identified by the increase of interlaminar shear strength (ILSS). In particular, the Gd addition promoted the ILSS and bending strength greatly, with an increase by 60.4% and 25.3% compared with Cf/Mg composite, respectively. The fracture surfaces of the composites were examined by scanning electron microscopy and micrographs were employed to explain the inherent relation between interface characterization and mechanical properties.
In the current work an attempt has been made to synthesize novel high surface area nano-TiO2 mate... more In the current work an attempt has been made to synthesize novel high surface area nano-TiO2 materials (titanium dioxide nanoparticles/TNPs and nanostructured or mesoporous titanium dioxide using KIT-6 silica template/Meso. TiO2) in order to establish the photocatalytic reduction of CO2 greenhouse gas in the presence of H2O vapor to produce hydrocarbons and syngas. The synthesized materials have been characterized through N2-adsorption/desorption, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and ultraviolet–visible (UV–Vis) spectroscopy analysis techniques. The TNPs consists of an average 11 nm of TiO2 particles, shows a higher surface area of 151 m2/g than the commercial Aeroxide P25 TiO2 (53 m2/g), and also demonstrates an enhanced adsorption capacity. However, the Meso. TiO2 has shown a higher surface area (190 m2/g) and mesoporosity (4 nm pores) than the TNPs and Aeroxide P25 TiO2, as confirmed by the characterizations. In the reaction, the TNPs with the enhanced adsorption capability, due to the high surface area and smaller nano-sized particle morphology, showed a higher syngas (CO, H2) production than the commercial Aeroxide P25 TiO2. However, the novel Meso. TiO2 showed more hydrocarbons (CH4, CH3OH) and a higher syngas production together with better reaction kinetics and stability due to its better characteristics than the commercial Aeroxide P25 TiO2. The key parameters that affect the activity have been optimized to increase fuel production. The reaction mechanism indicates competitive adsorption of CO2 and H2O vapors on the catalyst surface. The key parameters including the UV light source and UV intensity, H2O/CO2 ratios and catalyst shapes influence the catalytic performance, and therefore, these parameters have been optimized to increase the fuel products. Partial saturation of the active adsorption sites and the oxygen produced are the possible causes of the deactivation, however, the catalysts can be regenerated quickly through a simple evaporation technique.
Compressed Natural Gas (CNG) engines are growing in interest in the car market due to their abili... more Compressed Natural Gas (CNG) engines are growing in interest in the car market due to their ability in the limitation of NOx and CO2 emissions. Unburned methane is harder to oxidize than gasoline-derived unconverted HCs and its strong greenhouse effect induces the development of tailored after treatment technologies. In this work, SBA-15 and in particular KIT-6 have been used as supports for Pd catalysts for the abatement of methane emitted by CNG engines. The synthesized materials have been characterized through XRD, N2-adsorption/desorption, EDX, STEM, and TEM analysis techniques. The influence of different pore structure and size of the mesoporous supports as well as of different Pd loading (in the range 0.25–0.7 wt%) on the activity has been investigated. All mesoporous silica supported Pd catalysts showed almost complete conversion of methane, although catalysts with the lowest Pd loadings reached 90% of conversion over 650 °C, whereas the maximum Pd loadings allowed to decrease the temperature of complete conversion, with T90 at 405 °C by employing the KIT-6 mesoporous silica support.
In the present work, novel isolated Ti-SBA-15-spherical and Ti-KIT-6 (Si/Ti = 200, 100 and 50) ph... more In the present work, novel isolated Ti-SBA-15-spherical and Ti-KIT-6 (Si/Ti = 200, 100 and 50) photocatalysts have been synthesized; optimized through N2-adsorption/desorption, SEM, EDX, UV–Vis, FT-IR, XPS and TEM analysis techniques; and explored for the photocatalytic reduction of greenhouse gas CO2 to renewable fuels. The Ti-KIT-6 (Si/Ti = 100) showed better CH4 production rate (4.15 μmol gcat.−1 h−1) than the corresponding Ti-KIT-6-dried (2.63 μmol gcat.−1 h−1) and the Ti-SBA-15-calcined/dried (1.85, 3.45 μmol gcat.−1 h−1, respectively) in the initial optimization reactions. CH3OH, CO, and H2 are the other main fuel products produced by the Ti-KIT-6-calcined (Si/Ti = 100). The increased surface concentration of OH groups found in the Ti-KIT-6-calcined (Si/Ti = 100) than the other two ratios (Si/Ti = 200, 50), the presence of more accessible surface reaction active sites due to the lower number of Ti–O–Ti or TiO2 agglomerates, and the more isolated Ti species which are uniformly dispersed on the 3-D KIT-6 mesoporous silica support without collapsing the mesoporous structure, have boosted the higher activity, which is even higher than the best commercial Aeroxide P25 TiO2. The reaction has been preceded by the competitive adsorption of CO2 and H2O vapors. The UV light source/intensity, H2O/CO2 ratios and catalyst shapes are the key factors that influence the performance of the catalyst, and therefore, these parameters have been optimized to boost the fuel products.
Thermal conductivity of SiCp/Cu composites was usually far below the expectation, which is usuall... more Thermal conductivity of SiCp/Cu composites was usually far below the expectation, which is usually attributed to the low real thermal conductivity of matrix. In the present work, highly pure Cu matrix composites reinforced with acid washed SiC particles were prepared by the pressure infiltration method. The interfacial microstructure of SiCp/Cu composites was characterized by layered interfacial products, including un-reacted SiC particles, a Cu–Si layer, a polycrystalline C layer and Cu–Si matrix. However, no Cu3Si was found in the present work, which is evidence for the hypothesis that the formation of Cu3Si phase in SiC/Cu system might be related to the alloying elements in Cu matrix and residual Si in SiC particles. The thermal conductivity of SiCp/Cu composites was slightly increased with the particle size from 69.9 to 78.6 W/(m K). Due to high density defects, the real thermal conductivity of Cu matrix calculated by H–J model was only about 70 W/(m K). The significant decrease in thermal conductivity of Cu matrix is an important factor for the low thermal conductivity of SiCp/Cu composites. However, even considered the significant decrease of thermal conductivity of Cu matrix, theoretical values of SiCp/Cu composites calculated by H–J model were still higher than the experimental results. Therefore, an ideal particle was introduced in the present work to evaluate the effect of interfacial thermal resistance. The reverse-deduced effective thermal conductivities of ideal particles according to H–J model was about 80 W/(m K). Therefore, severe interfacial reaction in SiCp/Cu composites also leads to the low thermal conductivity of SiCp/Cu composites.
In this work, new nanoporous silica (Korea Advanced Institute of Science and Technology-6 (KIT-6)... more In this work, new nanoporous silica (Korea Advanced Institute of Science and Technology-6 (KIT-6)-dried or KIT-6-calcined) incorporated with isolated Ti materials with different Si/Ti ratios (Si/Ti = 200, 100, and 50) has been synthesized and investigated to establish photocatalytic reduction of CO2 in the presence of H2O vapors. The properties of the materials have been characterized through N2 adsorption/desorption, UV-vis, TEM, FT-IR, and XPS analysis techniques. The intermediate amount of the isolated Ti (Si/Ti = 100) has resulted to be more uniformly distributed on the surface and within the three-dimensional pore structure of the KIT-6 material, without its structure collapsing, than the other two ratios (Si/Ti = 200 and 50). However, titania agglomerates have been observed to have formed due to the increased Ti content (Si/Ti = 50). The Ti-KIT-6 (calcined) materials in the reaction showed higher activity than the Ti-KIT-6 (dried) materials, which produced CH4, H2, CO, and CH3OH (vapors) as fuel products. The Ti-KIT-6 (Si/Ti = 100) material also showed more OH groups, which are useful to obtain a higher production rate of the products, particularly methane, which was even higher than the rate of the best commercial TiO2 (Aeroxide P25, Evonik Industries AG, Essen, Germany) photocatalyst.
Photocatalysis is attracting more and more interest because it offers efficient environmental fri... more Photocatalysis is attracting more and more interest because it offers efficient environmental friendly exploitation of solar energy for several end uses. In this context, research into the reactivity of photocatalysts on surfaces is of considerable importance. In this paper, the introduction of ammonium carbonate, a cost-effective and nontoxic reagent, is shown to influence preferential crystal growth of the photocatalyst BiVO4 along its {040} facet at high pH, thereby increasing the concentration of OH species on its surface, resulting in a substantial improvement in its visible-light-induced photocatalytic activity. As a result, 6 times higher rate of photoinduced degradation of ethylene has been measured compared to the best rate obtained with TiO2 photocatalyst ever produced by our group and even 10 times higher than with the reference Degussa P25 titania.
ABSTRACT SiC nanowires have been rarely investigated or explored along their axial direction by t... more ABSTRACT SiC nanowires have been rarely investigated or explored along their axial direction by transmission electron microscopy (TEM). Here we report the investigation of the cross-section microstructure of SiC nanowires by embedding them into Al matrix. Morphology of SiC nanowires was cylindrical with smooth surface or bamboo shape. Cubic (3C-SiC) and hexagonal structure (2H-SiC) phases were detected by X-ray diffraction (XRD) analysis. High density stacking faults were observed in both the cylindrical and bamboo shaped nanowires which were perpendicular to their axial direction. Selected area electron diffraction (SAED) patterns of the cylindrical and bamboo shaped SiC nanowires both in the perpendicular and parallel direction to the axial direction were equivalent in the structure. After calculation and remodeling, it has been found that the SAED patterns were composed of two sets of diffraction patterns, corresponding to 2H-SiC and 3C-SiC, respectively. Therefore, it could be concluded that the SiC nanowires are composed of a large number of small fragments that are formed by hybrid 3C-SiC and 2H-SiC structures.
ABSTRACT Al matrix composites reinforced with one-dimensional nano-materials (for instance nanotu... more ABSTRACT Al matrix composites reinforced with one-dimensional nano-materials (for instance nanotubes, nanowires and nanofibres) have been widely investigated in the past decade. However, the preparation, microstructure and mechanical behavior of high content (>10 vol%) SiC nanowires reinforced Al (SiCnw/Al) has not been reported yet. In the present work, 15 vol% SiCnw/6061Al composite was prepared by the pressure infiltration method. SiCnw/6061Al composite demonstrated good machining performance since continuous chip was obtained after cut by carbide turning tools. SiC nanowires were uniformly distributed without any observance of SiC agglomerates. Long SiC nanowires were observed after etching, implying that the preparation process had shown minor damage to the SiC nanowires and therefore, the pressure infiltration method is a feasible and successful way to prepare high content SiCnw/Al composites. The interface between SiC nanowires and Al was well bonded, and no significant interfacial product was found. After aging treatment, 15 vol% SiCnw/6061Al composite demonstrated high strength (over 1000 MPa), while a comparable plasticity as Al matrix was retained. The strengthening effect of SiC nanowires could be fully utilized through the fracture of SiC nanowires. Moreover, the grain size of Al matrix in SiCnw/6061Al composite was significantly refined and polycrystalline diffraction rings were observed. Therefore, supplemented to previous results in one-dimensional nano-materials reinforced Al matrix composites, fine-grain was also found as another main strengthening mechanism.
A set of Rh-containing catalysts (Rh-MCM-41, Rh-SBA-15, Rh-KIT-6 and Rh-MCF, nominal Rh content =... more A set of Rh-containing catalysts (Rh-MCM-41, Rh-SBA-15, Rh-KIT-6 and Rh-MCF, nominal Rh content = 1 wt.%) has been prepared by wet impregnation of mesoporous silicas and tested for high concentration N2O abatement. The physico-chemical properties of the materials have been investigated by means of complementary techniques.
The best performances, in terms of N2O decomposition, have been achieved for the Rh-MCF catalyst, due to the better textural properties of the MCF silica. In fact, the MCF-type support exhibits three-dimensional mesoporosity with ultra-large cells (up to 40 nm), which allow a uniform distribution of small RhOx particles (≈1 nm) over the high (internal) surface area of the MCF. Moreover, the Rh active sites are also readily accessible to N2O molecules.
The most promising catalyst has shown the highest amount of Rh1+ species, the easiest rhodium reducibility and the greatest abundance of Rh surface sites. These important features reflect the different Rh particle sizes and play a role in catalytic activity.
A remarkable relationship between the catalytic activity and the dimension of the RhOx particles has been observed in the 1–2.5 nm size domain, thus confirming the dispersion-sensitivity of N2O decomposition over RhOx nanoparticles.
Nanostructured TiO2/KIT-6 catalysts with different concentrations of incorporated TiO2, have been... more Nanostructured TiO2/KIT-6 catalysts with different concentrations of incorporated TiO2, have been synthesized, characterized, and examined in order to improve the photocatalytic reduction of carbon dioxide (CO2) feedstock with water vapor (H2O) to produce tunable value-added energy products. Nanostructured TiO2, dispersed on KIT-6 (three-dimensional mesoporous silica), was found to be present in both the silica framework and on the surface, where it produced large surface area photocatalysts with enhanced adsorption capability of the reactants to photocatalytically convert into CH4, CH3OH (hydrocarbons) and CO, H2 (similar to syngas). The formed products were influenced directly by the dispersed TiO2 concentration as well as by the calcination temperature. Hydrocarbon and CO formation as well as the reaction kinetics improved as the TiO2 concentration was increased from 1 to 20 wt%. However, a further increase in TiO2 loadings (to 90%) decreased the hydrocarbon and CO, and increased H2 formation. The highest optimization toward hydrocabon selectivity was shown by 20 wt% TiO2, while a 90 wt% TiO2 loading was more selective for H2 formation. This was likely due to the uniform dispersion and stabilization of the anatase TiO2 with 20 wt% on KIT-6, which in turn allowed more CO2 adsorption and a better light penetration than 90% TiO2/KIT-6 in which it showed a bulk phase and large agglomerates with light penetration limitations that were more favorable for H2O adsorption. A reaction mechanism, which has helped to understand these findings, has been proposed. Moreover, a 24 h activity test with the optimized 20 wt% TiO2/KIT-6 showed an increase in the product yield but only a minor, gradual decrease in the reaction rate, which points out that these photocatalysts could be promising for turning CO2 greenhouse gas feedstock into selective renewable energy products.
Matrix alloying is an effective and convenient method to improve the interface bonding strength f... more Matrix alloying is an effective and convenient method to improve the interface bonding strength for continuous carbon fiber reinforced magnesium matrix composites. In this work, rare earth metal Gd was selected as an alloying element to improve the interface bonding of Cf/Mg composite. Cf/Mg composites with different Gd content were fabricated by pressure infiltration method. The effect of Gd addition on the interfacial microstructures and mechanical properties of the composites were investigated. The results showed that the rare earth Gd tended to segregate at interface area to form Gd2O3 layer and particle phase Mg7Gd. Both the interfacial products enhanced the interface bonding strength which can be identified by the increase of interlaminar shear strength (ILSS). In particular, the Gd addition promoted the ILSS and bending strength greatly, with an increase by 60.4% and 25.3% compared with Cf/Mg composite, respectively. The fracture surfaces of the composites were examined by scanning electron microscopy and micrographs were employed to explain the inherent relation between interface characterization and mechanical properties.
In the current work an attempt has been made to synthesize novel high surface area nano-TiO2 mate... more In the current work an attempt has been made to synthesize novel high surface area nano-TiO2 materials (titanium dioxide nanoparticles/TNPs and nanostructured or mesoporous titanium dioxide using KIT-6 silica template/Meso. TiO2) in order to establish the photocatalytic reduction of CO2 greenhouse gas in the presence of H2O vapor to produce hydrocarbons and syngas. The synthesized materials have been characterized through N2-adsorption/desorption, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and ultraviolet–visible (UV–Vis) spectroscopy analysis techniques. The TNPs consists of an average 11 nm of TiO2 particles, shows a higher surface area of 151 m2/g than the commercial Aeroxide P25 TiO2 (53 m2/g), and also demonstrates an enhanced adsorption capacity. However, the Meso. TiO2 has shown a higher surface area (190 m2/g) and mesoporosity (4 nm pores) than the TNPs and Aeroxide P25 TiO2, as confirmed by the characterizations. In the reaction, the TNPs with the enhanced adsorption capability, due to the high surface area and smaller nano-sized particle morphology, showed a higher syngas (CO, H2) production than the commercial Aeroxide P25 TiO2. However, the novel Meso. TiO2 showed more hydrocarbons (CH4, CH3OH) and a higher syngas production together with better reaction kinetics and stability due to its better characteristics than the commercial Aeroxide P25 TiO2. The key parameters that affect the activity have been optimized to increase fuel production. The reaction mechanism indicates competitive adsorption of CO2 and H2O vapors on the catalyst surface. The key parameters including the UV light source and UV intensity, H2O/CO2 ratios and catalyst shapes influence the catalytic performance, and therefore, these parameters have been optimized to increase the fuel products. Partial saturation of the active adsorption sites and the oxygen produced are the possible causes of the deactivation, however, the catalysts can be regenerated quickly through a simple evaporation technique.
Compressed Natural Gas (CNG) engines are growing in interest in the car market due to their abili... more Compressed Natural Gas (CNG) engines are growing in interest in the car market due to their ability in the limitation of NOx and CO2 emissions. Unburned methane is harder to oxidize than gasoline-derived unconverted HCs and its strong greenhouse effect induces the development of tailored after treatment technologies. In this work, SBA-15 and in particular KIT-6 have been used as supports for Pd catalysts for the abatement of methane emitted by CNG engines. The synthesized materials have been characterized through XRD, N2-adsorption/desorption, EDX, STEM, and TEM analysis techniques. The influence of different pore structure and size of the mesoporous supports as well as of different Pd loading (in the range 0.25–0.7 wt%) on the activity has been investigated. All mesoporous silica supported Pd catalysts showed almost complete conversion of methane, although catalysts with the lowest Pd loadings reached 90% of conversion over 650 °C, whereas the maximum Pd loadings allowed to decrease the temperature of complete conversion, with T90 at 405 °C by employing the KIT-6 mesoporous silica support.
In the present work, novel isolated Ti-SBA-15-spherical and Ti-KIT-6 (Si/Ti = 200, 100 and 50) ph... more In the present work, novel isolated Ti-SBA-15-spherical and Ti-KIT-6 (Si/Ti = 200, 100 and 50) photocatalysts have been synthesized; optimized through N2-adsorption/desorption, SEM, EDX, UV–Vis, FT-IR, XPS and TEM analysis techniques; and explored for the photocatalytic reduction of greenhouse gas CO2 to renewable fuels. The Ti-KIT-6 (Si/Ti = 100) showed better CH4 production rate (4.15 μmol gcat.−1 h−1) than the corresponding Ti-KIT-6-dried (2.63 μmol gcat.−1 h−1) and the Ti-SBA-15-calcined/dried (1.85, 3.45 μmol gcat.−1 h−1, respectively) in the initial optimization reactions. CH3OH, CO, and H2 are the other main fuel products produced by the Ti-KIT-6-calcined (Si/Ti = 100). The increased surface concentration of OH groups found in the Ti-KIT-6-calcined (Si/Ti = 100) than the other two ratios (Si/Ti = 200, 50), the presence of more accessible surface reaction active sites due to the lower number of Ti–O–Ti or TiO2 agglomerates, and the more isolated Ti species which are uniformly dispersed on the 3-D KIT-6 mesoporous silica support without collapsing the mesoporous structure, have boosted the higher activity, which is even higher than the best commercial Aeroxide P25 TiO2. The reaction has been preceded by the competitive adsorption of CO2 and H2O vapors. The UV light source/intensity, H2O/CO2 ratios and catalyst shapes are the key factors that influence the performance of the catalyst, and therefore, these parameters have been optimized to boost the fuel products.
Thermal conductivity of SiCp/Cu composites was usually far below the expectation, which is usuall... more Thermal conductivity of SiCp/Cu composites was usually far below the expectation, which is usually attributed to the low real thermal conductivity of matrix. In the present work, highly pure Cu matrix composites reinforced with acid washed SiC particles were prepared by the pressure infiltration method. The interfacial microstructure of SiCp/Cu composites was characterized by layered interfacial products, including un-reacted SiC particles, a Cu–Si layer, a polycrystalline C layer and Cu–Si matrix. However, no Cu3Si was found in the present work, which is evidence for the hypothesis that the formation of Cu3Si phase in SiC/Cu system might be related to the alloying elements in Cu matrix and residual Si in SiC particles. The thermal conductivity of SiCp/Cu composites was slightly increased with the particle size from 69.9 to 78.6 W/(m K). Due to high density defects, the real thermal conductivity of Cu matrix calculated by H–J model was only about 70 W/(m K). The significant decrease in thermal conductivity of Cu matrix is an important factor for the low thermal conductivity of SiCp/Cu composites. However, even considered the significant decrease of thermal conductivity of Cu matrix, theoretical values of SiCp/Cu composites calculated by H–J model were still higher than the experimental results. Therefore, an ideal particle was introduced in the present work to evaluate the effect of interfacial thermal resistance. The reverse-deduced effective thermal conductivities of ideal particles according to H–J model was about 80 W/(m K). Therefore, severe interfacial reaction in SiCp/Cu composites also leads to the low thermal conductivity of SiCp/Cu composites.
In this work, new nanoporous silica (Korea Advanced Institute of Science and Technology-6 (KIT-6)... more In this work, new nanoporous silica (Korea Advanced Institute of Science and Technology-6 (KIT-6)-dried or KIT-6-calcined) incorporated with isolated Ti materials with different Si/Ti ratios (Si/Ti = 200, 100, and 50) has been synthesized and investigated to establish photocatalytic reduction of CO2 in the presence of H2O vapors. The properties of the materials have been characterized through N2 adsorption/desorption, UV-vis, TEM, FT-IR, and XPS analysis techniques. The intermediate amount of the isolated Ti (Si/Ti = 100) has resulted to be more uniformly distributed on the surface and within the three-dimensional pore structure of the KIT-6 material, without its structure collapsing, than the other two ratios (Si/Ti = 200 and 50). However, titania agglomerates have been observed to have formed due to the increased Ti content (Si/Ti = 50). The Ti-KIT-6 (calcined) materials in the reaction showed higher activity than the Ti-KIT-6 (dried) materials, which produced CH4, H2, CO, and CH3OH (vapors) as fuel products. The Ti-KIT-6 (Si/Ti = 100) material also showed more OH groups, which are useful to obtain a higher production rate of the products, particularly methane, which was even higher than the rate of the best commercial TiO2 (Aeroxide P25, Evonik Industries AG, Essen, Germany) photocatalyst.
Photocatalysis is attracting more and more interest because it offers efficient environmental fri... more Photocatalysis is attracting more and more interest because it offers efficient environmental friendly exploitation of solar energy for several end uses. In this context, research into the reactivity of photocatalysts on surfaces is of considerable importance. In this paper, the introduction of ammonium carbonate, a cost-effective and nontoxic reagent, is shown to influence preferential crystal growth of the photocatalyst BiVO4 along its {040} facet at high pH, thereby increasing the concentration of OH species on its surface, resulting in a substantial improvement in its visible-light-induced photocatalytic activity. As a result, 6 times higher rate of photoinduced degradation of ethylene has been measured compared to the best rate obtained with TiO2 photocatalyst ever produced by our group and even 10 times higher than with the reference Degussa P25 titania.
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The best performances, in terms of N2O decomposition, have been achieved for the Rh-MCF catalyst, due to the better textural properties of the MCF silica. In fact, the MCF-type support exhibits three-dimensional mesoporosity with ultra-large cells (up to 40 nm), which allow a uniform distribution of small RhOx particles (≈1 nm) over the high (internal) surface area of the MCF. Moreover, the Rh active sites are also readily accessible to N2O molecules.
The most promising catalyst has shown the highest amount of Rh1+ species, the easiest rhodium reducibility and the greatest abundance of Rh surface sites. These important features reflect the different Rh particle sizes and play a role in catalytic activity.
A remarkable relationship between the catalytic activity and the dimension of the RhOx particles has been observed in the 1–2.5 nm size domain, thus confirming the dispersion-sensitivity of N2O decomposition over RhOx nanoparticles.
The best performances, in terms of N2O decomposition, have been achieved for the Rh-MCF catalyst, due to the better textural properties of the MCF silica. In fact, the MCF-type support exhibits three-dimensional mesoporosity with ultra-large cells (up to 40 nm), which allow a uniform distribution of small RhOx particles (≈1 nm) over the high (internal) surface area of the MCF. Moreover, the Rh active sites are also readily accessible to N2O molecules.
The most promising catalyst has shown the highest amount of Rh1+ species, the easiest rhodium reducibility and the greatest abundance of Rh surface sites. These important features reflect the different Rh particle sizes and play a role in catalytic activity.
A remarkable relationship between the catalytic activity and the dimension of the RhOx particles has been observed in the 1–2.5 nm size domain, thus confirming the dispersion-sensitivity of N2O decomposition over RhOx nanoparticles.