Major challenges encountered when developing manganese-based materials for ozone decomposition ar... more Major challenges encountered when developing manganese-based materials for ozone decomposition are related to the low stability and water inactivation. To solve these problems, a hierarchical structure consisted of graphene encapsulating α-MnO2 nanofiber was developed. The optimized catalyst exhibited a stable ozone conversion efficiency of 80% and excellent stability over 100 h under a relative humidity (RH) of 20%. Even though the RH increased to 50%, the ozone conversion also reached 70%, well beyond the performance of α-MnO2 nanofiber. Here, surface graphite carbon was activated by capturing the electron from inner unsaturated Mn atoms. The excellent stability originated from the moderate local work function, which compromised the reaction barriers in the adsorption of ozone molecule and the desorption of the intermediate oxygen species. The hydrophobic graphene shells hindered the chemisorption of water vapour, consequently enhanced its water resistance. This work offered insig...
Highly efficient Pt–Fe/c-Al2O3 catalysts for preferential oxidation of CO in excess of H2 (CO-PRO... more Highly efficient Pt–Fe/c-Al2O3 catalysts for preferential oxidation of CO in excess of H2 (CO-PROX) were prepared by utilizing single- atom Fe species as active sites for O2 activation, which exhibited high catalytic activity and selectivity from 25 8C to 200 8C, with the highest Pt specific rate of Pt-based catalysts for CO-PROX.
Supported metal single atoms have demonstrated excellent catalytic performance for many chemical ... more Supported metal single atoms have demonstrated excellent catalytic performance for many chemical transformations. The effects of support on the catalytic performance of supported single metal atoms, however, have not been clearly elucidated. We carried out a systematic investigation of the effects of supports on CO oxidation by single Pt (Pt 1) atoms dispersed on different metal oxides: highly reducible Fe 2 O 3 , reducible ZnO, and irreducible γ-Al 2 O 3. It was found that Pt 1 atoms on three metal oxides are active for CO oxidation, and the chemical properties of supports determine the catalytic performance of Pt 1 single-atom catalysts (SACs). Both the presence of −OH groups on support surfaces and the addition of H 2 O significantly modify CO oxidation on three SACs and reduce the effects of supports on their catalytic performances. We conclude that the interaction between single metal atoms and support as well as surface properties of supports control the catalytic behavior of SACs.
Supported metal single atoms have demonstrated excellent catalytic performance for many chemical ... more Supported metal single atoms have demonstrated excellent catalytic performance for many chemical transformations. The effects of support on the catalytic performance of supported single metal atoms, however, have not been clearly elucidated. We carried out a systematic investigation of the effects of supports on CO oxidation by single Pt (Pt 1) atoms dispersed on different metal oxides: highly reducible Fe 2 O 3 , reducible ZnO, and irreducible γ-Al 2 O 3. It was found that Pt 1 atoms on three metal oxides are active for CO oxidation, and the chemical properties of supports determine the catalytic performance of Pt 1 single-atom catalysts (SACs). Both the presence of −OH groups on support surfaces and the addition of H 2 O significantly modify CO oxidation on three SACs and reduce the effects of supports on their catalytic performances. We conclude that the interaction between single metal atoms and support as well as surface properties of supports control the catalytic behavior of SACs.
The Co 3 O 4 and Bi 2 O 3 –Co 3 O 4 were prepared by precipitation and co-precipitation method. T... more The Co 3 O 4 and Bi 2 O 3 –Co 3 O 4 were prepared by precipitation and co-precipitation method. The samples were characterized by XRD, BET, H 2-TPR, Raman, XPS and EPR. The low-temperature CO oxidation on the catalysts was also investigated. The results showed the deposition of Bi 2 O 3 enhanced the activity and stability of Co 3 O 4 for CO oxidation. 20 wt.% Bi 2 O 3 –Co 3 O 4 could completely convert CO as low as −89 • C, and maintain the complete oxidation of CO at −75 • C for 10 h. XRD and Raman results showed Bi 2 O 3 could enter the lattice of Co 3 O 4 , and promote the formation of the lattice distortion and structural defect. H 2-TPR results showed that reduction of Co 3 O 4 was promoted and the diffusion of oxygen was accelerated. XPS and EPR results showed the surface richness of Co 3+ and the increase of Co 2+ in 20 wt.% Bi 2 O 3 –Co 3 O 4. The formation of more Co 2+ in 20 wt.% Bi 2 O 3 –Co 3 O 4 could produce structure defects and lead to the formation of more oxygen vacancy, which was suggested to play the critical role in promoting the catalytic activity and stability of 20 wt.% Bi 2 O 3 –Co 3 O 4 .
The doping of In 2 O 3 significantly promoted the catalytic performance of Co 3 O 4 for CO oxidat... more The doping of In 2 O 3 significantly promoted the catalytic performance of Co 3 O 4 for CO oxidation. The activities of In 2 O 3 −Co 3 O 4 increased with an increase in In 2 O 3 content, in the form of a volcano curve. Twenty-five wt % In 2 O 3 −Co 3 O 4 (25 InCo) showed the highest CO oxidation activity, which could completely convert CO to CO 2 at a temperature as low as −105 °C, whereas it was only −40 °C over pure Co 3 O 4. The doping of In 2 O 3 induced the expansion of the unit cell and structural distortion of Co 3 O 4 , which was confirmed by the slight elongation of the Co−O bond obtained from EXAFS data. The red shift of the UV−vis absorption illustrated that the electron transfer from O 2− to Co 3+ /Co 2+ became easier and implied that the bond strength of Co−O was weakened, which promoted the activation of oxygen. Low-temperature H 2-TPR and O 2-TPD results also revealed that In 2 O 3 −Co 3 O 4 behaved with excellent redox ability. The XANES, XPS, XPS valence band, and FT-IR data exhibited that the CO adsorption strength became weaker due to the downshift of the d-band center, which correspondingly weakened the adsorption of CO 2 and obviously inhibited the accumulation of surface carbonate species. In short, the doping of In 2 O 3 induced the structural defects, modified the surface electronic structure, and promoted the redox ability of Co 3 O 4 , which tuned the adsorption strength of CO and oxygen activation simultaneously.
CO adsorption and O 2 activation played important roles in CO oxidation on a supported Pd catalys... more CO adsorption and O 2 activation played important roles in CO oxidation on a supported Pd catalyst, which were dependent on the chemical state of Pd. A series of Pd catalysts supported on Al 2 O 3 with different Pd states were prepared: metal Pd (NCR), PdO (NC), Pd 2+ coordinated with Cl − (Pd 2+ –Cl − , CF), and a mixture of PdO and Pd 2+ –Cl − (CC) and the activity of CO oxidation was in the order NCR ~ CF > CC ≫ NC. The catalysts were characterized by Brunauer, Emmett and Teller (BET) surface area analysis, X-ray diffraction (XRD), temperature programmed reduction by hydrogen (H 2-TPR), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results showed that metal Pd (Pd 0) could be partially oxidized to Pd + in the presence of O 2 , which produced new CO adsorp-tion sites and decreased the CO adsorption strength simultaneously. The cooperation between the enhanced CO adsorption and the decrease in the CO adsorption strength led to high activity for CO oxidation on NCR. For high chemical valence Pd in the species (Pd 2+), the chemical environment or coordinated ligand of the Pd species showed large effects on the CO oxidation. The lowest CO oxidation activity on NC occurred when PdO hardly adsorbed CO, meanwhile, PdO was not easily reduced by CO. However, the presence of Cl − significantly promoted the reduction of Pd 2+ to Pd + , which increased the amount of CO adsorption and resulted in the higher activity for CO oxidation on CF and CC than PdO. Tuning the CO adsorption by adjusting the chemical state of Pd may be a useful approach to prepare a highly efficient supported Pd catalyst.
The modification of Co 3 O 4 by Bi 2 O 3 significantly enhanced its catalytic performance for CO ... more The modification of Co 3 O 4 by Bi 2 O 3 significantly enhanced its catalytic performance for CO oxidation. The 20 wt.% Bi 2 O 3-Co 3 O 4 exhibited the best catalytic performance. The results of H 2-TPR and CO-TPR revealed that the mobility of oxygen was accelerated greatly and the ability of low-temperature oxygen activation was the crucial factor to improve the catalytic performance. Bi 2 O 3 entered the lattice of Co 3 O 4 caused the structural defect and lattice distortion, which should be the origin of the high O 2 activation ability and mobility. Structure-performance correlation demonstrated that the low-temperature oxygen activation was dependent on the defective degree of structure, which was determined by the content of Bi 2 O 3. The catalytic behaviors under different reaction conditions revealed that CO could effectively adsorb on the surface active sites and CO 2 could competitively adsorb on the active sites. The ability to supply the active O 2 species was suggested to be a key step. The kinetic data showed not only the amount of surface active sites were increased on the surface of Co 3 O 4 but also the catalytic ability of single active site was enhanced greatly.
The supported Wacker-type catalysts were prepared with different original activated carbons (wood... more The supported Wacker-type catalysts were prepared with different original activated carbons (wood, coconut shell and coal based carbon) as supports, and the catalytic activities for CO oxidation with or without NO x were investigated. Nitrogen adsorption, temperature-programmed desorption (TPD) and Boehm titration results showed that wood based activated carbon had developed meso-/macropore structure and rich oxygen functional groups. Oxygen-containing surface groups benefited active sites Pd 2+ and Cu 2+ phase enriched on the catalyst surface which were confirmed by X-ray Photoelectron Spectroscopy (XPS). H 2 temperature-programmed reduction (H 2-TPR) experiments indicated that the oxygen-containing surface groups increased the ratio of copper species adjacent to palladium species and promoted the reducibility of Cu 2+ species. Density functional theory (DFT) calculation displayed that NO x was more active to combine with Pd 2+ component than CO did, which explained the presence of NO x had an obvious inhibition effect on CO oxidation.
COMMUNICATION Yun Guo, Guanzhong Lu et al. Ultralow-temperature CO oxidation on an In 2 O 3 –Co 3... more COMMUNICATION Yun Guo, Guanzhong Lu et al. Ultralow-temperature CO oxidation on an In 2 O 3 –Co 3 O 4 catalyst: a strategy to tune CO adsorption strength and oxygen activation simultaneously
Nanocrystal Au(1 1 1) 2-Propanol TPD STM Rutile(1 1 0) Nanoparticle a b s t r a c t The reactivit... more Nanocrystal Au(1 1 1) 2-Propanol TPD STM Rutile(1 1 0) Nanoparticle a b s t r a c t The reactivity of 2-propanol with TiO 2 nanocrystals supported on Au(1 1 1) was studied by temperature-programmed desorption (TPD) and scanning tunneling microscopy (STM). The nanocrystals, which are grown through oxidation of a TiAAu surface alloy, had an average height of 1 nm and width of 15 nm with a dominantly hexagonal morphology. The desorption of propanol and propanol-derived products from the TiO 2 nanocrystal surfaces was observed in the 270–570 K temperature range and could be distinguished from desorption of propanol from the Au(1 1 1) surface below 270 K. With increasing propanol coverage, the TiO 2-related TPD peaks were occupied before the appearance of any Au(1 1 1)-related peaks. Our calculations showed that the TiO 2 nanocrystals were saturated at 0.4 ML of local propanol surface concentration, where 1 ML 5.2 Â 10 14 cm À2 refers to surface density of five-coordinated Ti atoms on rutile(1 1 0). Our TPD measurements showed that 61% of this adsorbed propanol desorbed molecularly at 310 K, while 23% dehydrated into propene and 6% dehydrogenated to form acetone, both products desorbing in the 370–570 K temperature range. The desorption temperatures of products from supported TiO 2 nanocrystals were shown to depend strongly on the morphology of the nanocrystals.
Different pretreatments (wet, oxidation and complex pretreatments) were used to modify activated ... more Different pretreatments (wet, oxidation and complex pretreatments) were used to modify activated carbon honeycomb monolith, and the role of surface properties of support in CO oxidation over Pd/ACHM catalysts was also investigated. Pretreatment was an efficient way to introduce oxygen groups, especially by complex pretreatment. Oxygen-containing groups increased 1.7 times as much as that of original ACHM, and 86% conversion was obtained at 30 °C and 100% relative humidity on supported Pd catalyst prepared from modified ACHM. Oxygen-containing species on the support not only improved Pd dispersion but also affected Pd states. Compared with Pd dispersion, Pd states played a more important role in CO oxidation. The amount of low-valent Pd species (Pd 0 , Pd +1) on catalyst surface was consistent with CO oxidation activity. The presence of NO caused CO oxidation conversion to decrease by 15% which was attributed to the difference between NO and CO adsorption energy on Pd surfaces confirmed by density functional theory calculation. 90 days' 1000 m 3 /h pilot experiment results showed that the catalyst exhibited high activity and stability in the presence of moisture and NO x .
Pd/H-ZSM-5 catalysts could completely cata-lyze CH 4 to CO 2 at as low as 320 °C, while there is ... more Pd/H-ZSM-5 catalysts could completely cata-lyze CH 4 to CO 2 at as low as 320 °C, while there is no detectable catalytic activity for pure H-ZSM-5 at 320 °C and only a conversion of 40% could be obtained at 500 °C over pure H-ZSM-5. Both the theoretical and experimental results prove that surface acidic sites could facilitate the formation of active metal species as the anchoring sites, which could further modify the electronic and coordination structure of metal species. PdO x interacting with the surface Brö nsted acid sites of H-ZSM-5 could exhibit Lewis acidity and lower oxidation states, as proven by the XPS, XPS valence band, CO-DRIFTS, pyridine FT-IR, and NH 3-TPD data. Density functional theory calculations suggest PdO x groups to be the active sites for methane combustion, in the form of [AlO 2 ]Pd(OH)-ZSM-5. The stronger Lewis acidity of coordinatively unsaturated Pd and the stronger basicity of oxygen from anchored PdO x species are two key characteristics of the active sites ([AlO 2 ]Pd(OH)-ZSM-5) for methane combustion. As a result, the PdO x species anchored by Brønsted acid sites of H-ZSM-5 exhibit high performance for catalytic combustion of CH 4 over Pd/H-ZSM-5 catalysts.
Upgrading olefin in the synthetic oil to alkane is highly desired due to its high volatility and ... more Upgrading olefin in the synthetic oil to alkane is highly desired due to its high volatility and thermal unstability as well as low energy density. Unlike conventional hydrotreating, methane (CH 4) was used in this study as the novel hydrogen donor for olefin saturation. The significant increase of H/C atomic ratio of product oil from 1.69 ± 0.02 (over pure ZSM-5) to 2.04 ± 0.02 (over Ir/ZSM-5 (10.0)) and the alkane content up to 83.8 ± 2.1% in the upgraded oil indicated that methane could exhibit comparable catalytic performance to what hydrogen (H 2) did for olefin (1-Decene) upgrading over the developed bifunctional catalysts with low Ir loadings. The HRTEM and XPS data revealed that the highly dispersed metallic Ir particles with average size of 1.32 nm was coexisting with IrO 2 species. The synergic effects of Ir/IrO 2 obviously promoted the activation of methane, which supplied sufficient hydrogen for the saturation and stabilization of olefin. The results from BET indicated that the pore size and volume of the ZSM-5 support were increased upon Ir introduction, which provided more active sites for cracking olefin (1-decene). NH 3-TPD results suggested that the presence of highly dispersed Ir increased the amount of surface acidity, which enhanced the formation and stabilization of carbenium ion intermediates. As a result, the produced alkanes were mainly composed of cyclopentane-derived compounds, like propylcyclopentane, 3-methylbutyl-cyclopentane and 1,2,4-trimethyl-cyclopentane, which has great application potential as immersion fluid and additive in the field of optics and petroleum.
Alkene can be converted to cycloalkane under methane environment over Pd/H-ZSM-5. Highly disperse... more Alkene can be converted to cycloalkane under methane environment over Pd/H-ZSM-5. Highly dispersed PdO x species benefits methane activation. Strength and amount of surface acidity play important role in olefin upgrading. Methane has potential to act as alternative hydrogen donor for olefin saturation. a b s t r a c t Olefin content minimization is critical for the long-term storage and long-distance transportation of oil product, which is commonly achieved through hydrogen saturation at high pressure to form paraffin. In this study, a novel catalytic process is reported to convert olefin to cycloalkane under methane environment with high selectivity. The main components of the product oil collected over Pd/ZSM-5 catalysts during olefin model compound (i.e., 1-decene) upgrading are cyclopentane, 1-methylbutyl-and cyclopentane, hexyl-while there are more than 46 species identified in the liquid product from the run with H-ZSM-5 support engaged. The total selectivity of the aforementioned cycloalkane products is up to 91.3% when 0.27 wt% Pd/ZSM-5 catalyst is charged, thus making the product oil more profitable. The HRTEM and XPS data reveal that the highly dispersed palladium particles are in the form of PdO x. The results from pyridine FT-IR and NH 3-TPD indicate that these PdO x species anchored onto the surface acidic sites exhibit the moderate acidic feature of Lewis acidic sites, which enhances the formation and stabilization of carbenium ion intermediates generated from 1-decene cracking. The strong interaction between PdO x species and surface acidic sites could not only stabilize the particle size and modify the electronic structure of Pd species but also modulate the acidic properties of ZSM-5 support, leading to promoted methane activation which would not only release sufficient hydrogen donors for preventing olefin aromatization, but also inhibit the over-cracking of carbenium ions. As a result, the selectivity of catalyst assisted olefin cyclization under methane environment is greatly enhanced.
A novel strategy is reported in this study to design a novel bifunctional PdO x /H-ZSM-5 catalyst... more A novel strategy is reported in this study to design a novel bifunctional PdO x /H-ZSM-5 catalyst for selective hy-drogenation of olefin. PdO x species (basic oxides) anchored on the strong acidic sites (Brönsted acid sites) of ze-olite support could not only generate new acidic sites with moderate acidic strength but also exhibit good capability for H 2 activation and dissociation. The conversion of 1-decene is 100% and total selectivity of methyl -nonane is 98.4 ± 0.4% at 350 °C. Our research might provide a valuable approach to design a highly efficient bifunctional catalyst for olefin upgrading.
ABSTRACT The doping of In2O3 significantly promoted the catalytic performance of Co3O4 for CO oxi... more ABSTRACT The doping of In2O3 significantly promoted the catalytic performance of Co3O4 for CO oxidation. The activities of In2O3–Co3O4 increased with an increase in In2O3 content, in the form of a volcano curve. Twenty-five wt % In2O3–Co3O4 (25 InCo) showed the highest CO oxidation activity, which could completely convert CO to CO2 at a temperature as low as −105 °C, whereas it was only −40 °C over pure Co3O4. The doping of In2O3 induced the expansion of the unit cell and structural distortion of Co3O4, which was confirmed by the slight elongation of the Co–O bond obtained from EXAFS data. The red shift of the UV–vis absorption illustrated that the electron transfer from O2– to Co3+/Co2+ became easier and implied that the bond strength of Co–O was weakened, which promoted the activation of oxygen. Low-temperature H2-TPR and O2-TPD results also revealed that In2O3–Co3O4 behaved with excellent redox ability. The XANES, XPS, XPS valence band, and FT-IR data exhibited that the CO adsorption strength became weaker due to the downshift of the d-band center, which correspondingly weakened the adsorption of CO2 and obviously inhibited the accumulation of surface carbonate species. In short, the doping of In2O3 induced the structural defects, modified the surface electronic structure, and promoted the redox ability of Co3O4, which tuned the adsorption strength of CO and oxygen activation simultaneously.Keywords: Co3O4; In2O3; CO oxidation; CO adsorption strength; redox ability; surface carbonate species
Major challenges encountered when developing manganese-based materials for ozone decomposition ar... more Major challenges encountered when developing manganese-based materials for ozone decomposition are related to the low stability and water inactivation. To solve these problems, a hierarchical structure consisted of graphene encapsulating α-MnO2 nanofiber was developed. The optimized catalyst exhibited a stable ozone conversion efficiency of 80% and excellent stability over 100 h under a relative humidity (RH) of 20%. Even though the RH increased to 50%, the ozone conversion also reached 70%, well beyond the performance of α-MnO2 nanofiber. Here, surface graphite carbon was activated by capturing the electron from inner unsaturated Mn atoms. The excellent stability originated from the moderate local work function, which compromised the reaction barriers in the adsorption of ozone molecule and the desorption of the intermediate oxygen species. The hydrophobic graphene shells hindered the chemisorption of water vapour, consequently enhanced its water resistance. This work offered insig...
Highly efficient Pt–Fe/c-Al2O3 catalysts for preferential oxidation of CO in excess of H2 (CO-PRO... more Highly efficient Pt–Fe/c-Al2O3 catalysts for preferential oxidation of CO in excess of H2 (CO-PROX) were prepared by utilizing single- atom Fe species as active sites for O2 activation, which exhibited high catalytic activity and selectivity from 25 8C to 200 8C, with the highest Pt specific rate of Pt-based catalysts for CO-PROX.
Supported metal single atoms have demonstrated excellent catalytic performance for many chemical ... more Supported metal single atoms have demonstrated excellent catalytic performance for many chemical transformations. The effects of support on the catalytic performance of supported single metal atoms, however, have not been clearly elucidated. We carried out a systematic investigation of the effects of supports on CO oxidation by single Pt (Pt 1) atoms dispersed on different metal oxides: highly reducible Fe 2 O 3 , reducible ZnO, and irreducible γ-Al 2 O 3. It was found that Pt 1 atoms on three metal oxides are active for CO oxidation, and the chemical properties of supports determine the catalytic performance of Pt 1 single-atom catalysts (SACs). Both the presence of −OH groups on support surfaces and the addition of H 2 O significantly modify CO oxidation on three SACs and reduce the effects of supports on their catalytic performances. We conclude that the interaction between single metal atoms and support as well as surface properties of supports control the catalytic behavior of SACs.
Supported metal single atoms have demonstrated excellent catalytic performance for many chemical ... more Supported metal single atoms have demonstrated excellent catalytic performance for many chemical transformations. The effects of support on the catalytic performance of supported single metal atoms, however, have not been clearly elucidated. We carried out a systematic investigation of the effects of supports on CO oxidation by single Pt (Pt 1) atoms dispersed on different metal oxides: highly reducible Fe 2 O 3 , reducible ZnO, and irreducible γ-Al 2 O 3. It was found that Pt 1 atoms on three metal oxides are active for CO oxidation, and the chemical properties of supports determine the catalytic performance of Pt 1 single-atom catalysts (SACs). Both the presence of −OH groups on support surfaces and the addition of H 2 O significantly modify CO oxidation on three SACs and reduce the effects of supports on their catalytic performances. We conclude that the interaction between single metal atoms and support as well as surface properties of supports control the catalytic behavior of SACs.
The Co 3 O 4 and Bi 2 O 3 –Co 3 O 4 were prepared by precipitation and co-precipitation method. T... more The Co 3 O 4 and Bi 2 O 3 –Co 3 O 4 were prepared by precipitation and co-precipitation method. The samples were characterized by XRD, BET, H 2-TPR, Raman, XPS and EPR. The low-temperature CO oxidation on the catalysts was also investigated. The results showed the deposition of Bi 2 O 3 enhanced the activity and stability of Co 3 O 4 for CO oxidation. 20 wt.% Bi 2 O 3 –Co 3 O 4 could completely convert CO as low as −89 • C, and maintain the complete oxidation of CO at −75 • C for 10 h. XRD and Raman results showed Bi 2 O 3 could enter the lattice of Co 3 O 4 , and promote the formation of the lattice distortion and structural defect. H 2-TPR results showed that reduction of Co 3 O 4 was promoted and the diffusion of oxygen was accelerated. XPS and EPR results showed the surface richness of Co 3+ and the increase of Co 2+ in 20 wt.% Bi 2 O 3 –Co 3 O 4. The formation of more Co 2+ in 20 wt.% Bi 2 O 3 –Co 3 O 4 could produce structure defects and lead to the formation of more oxygen vacancy, which was suggested to play the critical role in promoting the catalytic activity and stability of 20 wt.% Bi 2 O 3 –Co 3 O 4 .
The doping of In 2 O 3 significantly promoted the catalytic performance of Co 3 O 4 for CO oxidat... more The doping of In 2 O 3 significantly promoted the catalytic performance of Co 3 O 4 for CO oxidation. The activities of In 2 O 3 −Co 3 O 4 increased with an increase in In 2 O 3 content, in the form of a volcano curve. Twenty-five wt % In 2 O 3 −Co 3 O 4 (25 InCo) showed the highest CO oxidation activity, which could completely convert CO to CO 2 at a temperature as low as −105 °C, whereas it was only −40 °C over pure Co 3 O 4. The doping of In 2 O 3 induced the expansion of the unit cell and structural distortion of Co 3 O 4 , which was confirmed by the slight elongation of the Co−O bond obtained from EXAFS data. The red shift of the UV−vis absorption illustrated that the electron transfer from O 2− to Co 3+ /Co 2+ became easier and implied that the bond strength of Co−O was weakened, which promoted the activation of oxygen. Low-temperature H 2-TPR and O 2-TPD results also revealed that In 2 O 3 −Co 3 O 4 behaved with excellent redox ability. The XANES, XPS, XPS valence band, and FT-IR data exhibited that the CO adsorption strength became weaker due to the downshift of the d-band center, which correspondingly weakened the adsorption of CO 2 and obviously inhibited the accumulation of surface carbonate species. In short, the doping of In 2 O 3 induced the structural defects, modified the surface electronic structure, and promoted the redox ability of Co 3 O 4 , which tuned the adsorption strength of CO and oxygen activation simultaneously.
CO adsorption and O 2 activation played important roles in CO oxidation on a supported Pd catalys... more CO adsorption and O 2 activation played important roles in CO oxidation on a supported Pd catalyst, which were dependent on the chemical state of Pd. A series of Pd catalysts supported on Al 2 O 3 with different Pd states were prepared: metal Pd (NCR), PdO (NC), Pd 2+ coordinated with Cl − (Pd 2+ –Cl − , CF), and a mixture of PdO and Pd 2+ –Cl − (CC) and the activity of CO oxidation was in the order NCR ~ CF > CC ≫ NC. The catalysts were characterized by Brunauer, Emmett and Teller (BET) surface area analysis, X-ray diffraction (XRD), temperature programmed reduction by hydrogen (H 2-TPR), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results showed that metal Pd (Pd 0) could be partially oxidized to Pd + in the presence of O 2 , which produced new CO adsorp-tion sites and decreased the CO adsorption strength simultaneously. The cooperation between the enhanced CO adsorption and the decrease in the CO adsorption strength led to high activity for CO oxidation on NCR. For high chemical valence Pd in the species (Pd 2+), the chemical environment or coordinated ligand of the Pd species showed large effects on the CO oxidation. The lowest CO oxidation activity on NC occurred when PdO hardly adsorbed CO, meanwhile, PdO was not easily reduced by CO. However, the presence of Cl − significantly promoted the reduction of Pd 2+ to Pd + , which increased the amount of CO adsorption and resulted in the higher activity for CO oxidation on CF and CC than PdO. Tuning the CO adsorption by adjusting the chemical state of Pd may be a useful approach to prepare a highly efficient supported Pd catalyst.
The modification of Co 3 O 4 by Bi 2 O 3 significantly enhanced its catalytic performance for CO ... more The modification of Co 3 O 4 by Bi 2 O 3 significantly enhanced its catalytic performance for CO oxidation. The 20 wt.% Bi 2 O 3-Co 3 O 4 exhibited the best catalytic performance. The results of H 2-TPR and CO-TPR revealed that the mobility of oxygen was accelerated greatly and the ability of low-temperature oxygen activation was the crucial factor to improve the catalytic performance. Bi 2 O 3 entered the lattice of Co 3 O 4 caused the structural defect and lattice distortion, which should be the origin of the high O 2 activation ability and mobility. Structure-performance correlation demonstrated that the low-temperature oxygen activation was dependent on the defective degree of structure, which was determined by the content of Bi 2 O 3. The catalytic behaviors under different reaction conditions revealed that CO could effectively adsorb on the surface active sites and CO 2 could competitively adsorb on the active sites. The ability to supply the active O 2 species was suggested to be a key step. The kinetic data showed not only the amount of surface active sites were increased on the surface of Co 3 O 4 but also the catalytic ability of single active site was enhanced greatly.
The supported Wacker-type catalysts were prepared with different original activated carbons (wood... more The supported Wacker-type catalysts were prepared with different original activated carbons (wood, coconut shell and coal based carbon) as supports, and the catalytic activities for CO oxidation with or without NO x were investigated. Nitrogen adsorption, temperature-programmed desorption (TPD) and Boehm titration results showed that wood based activated carbon had developed meso-/macropore structure and rich oxygen functional groups. Oxygen-containing surface groups benefited active sites Pd 2+ and Cu 2+ phase enriched on the catalyst surface which were confirmed by X-ray Photoelectron Spectroscopy (XPS). H 2 temperature-programmed reduction (H 2-TPR) experiments indicated that the oxygen-containing surface groups increased the ratio of copper species adjacent to palladium species and promoted the reducibility of Cu 2+ species. Density functional theory (DFT) calculation displayed that NO x was more active to combine with Pd 2+ component than CO did, which explained the presence of NO x had an obvious inhibition effect on CO oxidation.
COMMUNICATION Yun Guo, Guanzhong Lu et al. Ultralow-temperature CO oxidation on an In 2 O 3 –Co 3... more COMMUNICATION Yun Guo, Guanzhong Lu et al. Ultralow-temperature CO oxidation on an In 2 O 3 –Co 3 O 4 catalyst: a strategy to tune CO adsorption strength and oxygen activation simultaneously
Nanocrystal Au(1 1 1) 2-Propanol TPD STM Rutile(1 1 0) Nanoparticle a b s t r a c t The reactivit... more Nanocrystal Au(1 1 1) 2-Propanol TPD STM Rutile(1 1 0) Nanoparticle a b s t r a c t The reactivity of 2-propanol with TiO 2 nanocrystals supported on Au(1 1 1) was studied by temperature-programmed desorption (TPD) and scanning tunneling microscopy (STM). The nanocrystals, which are grown through oxidation of a TiAAu surface alloy, had an average height of 1 nm and width of 15 nm with a dominantly hexagonal morphology. The desorption of propanol and propanol-derived products from the TiO 2 nanocrystal surfaces was observed in the 270–570 K temperature range and could be distinguished from desorption of propanol from the Au(1 1 1) surface below 270 K. With increasing propanol coverage, the TiO 2-related TPD peaks were occupied before the appearance of any Au(1 1 1)-related peaks. Our calculations showed that the TiO 2 nanocrystals were saturated at 0.4 ML of local propanol surface concentration, where 1 ML 5.2 Â 10 14 cm À2 refers to surface density of five-coordinated Ti atoms on rutile(1 1 0). Our TPD measurements showed that 61% of this adsorbed propanol desorbed molecularly at 310 K, while 23% dehydrated into propene and 6% dehydrogenated to form acetone, both products desorbing in the 370–570 K temperature range. The desorption temperatures of products from supported TiO 2 nanocrystals were shown to depend strongly on the morphology of the nanocrystals.
Different pretreatments (wet, oxidation and complex pretreatments) were used to modify activated ... more Different pretreatments (wet, oxidation and complex pretreatments) were used to modify activated carbon honeycomb monolith, and the role of surface properties of support in CO oxidation over Pd/ACHM catalysts was also investigated. Pretreatment was an efficient way to introduce oxygen groups, especially by complex pretreatment. Oxygen-containing groups increased 1.7 times as much as that of original ACHM, and 86% conversion was obtained at 30 °C and 100% relative humidity on supported Pd catalyst prepared from modified ACHM. Oxygen-containing species on the support not only improved Pd dispersion but also affected Pd states. Compared with Pd dispersion, Pd states played a more important role in CO oxidation. The amount of low-valent Pd species (Pd 0 , Pd +1) on catalyst surface was consistent with CO oxidation activity. The presence of NO caused CO oxidation conversion to decrease by 15% which was attributed to the difference between NO and CO adsorption energy on Pd surfaces confirmed by density functional theory calculation. 90 days' 1000 m 3 /h pilot experiment results showed that the catalyst exhibited high activity and stability in the presence of moisture and NO x .
Pd/H-ZSM-5 catalysts could completely cata-lyze CH 4 to CO 2 at as low as 320 °C, while there is ... more Pd/H-ZSM-5 catalysts could completely cata-lyze CH 4 to CO 2 at as low as 320 °C, while there is no detectable catalytic activity for pure H-ZSM-5 at 320 °C and only a conversion of 40% could be obtained at 500 °C over pure H-ZSM-5. Both the theoretical and experimental results prove that surface acidic sites could facilitate the formation of active metal species as the anchoring sites, which could further modify the electronic and coordination structure of metal species. PdO x interacting with the surface Brö nsted acid sites of H-ZSM-5 could exhibit Lewis acidity and lower oxidation states, as proven by the XPS, XPS valence band, CO-DRIFTS, pyridine FT-IR, and NH 3-TPD data. Density functional theory calculations suggest PdO x groups to be the active sites for methane combustion, in the form of [AlO 2 ]Pd(OH)-ZSM-5. The stronger Lewis acidity of coordinatively unsaturated Pd and the stronger basicity of oxygen from anchored PdO x species are two key characteristics of the active sites ([AlO 2 ]Pd(OH)-ZSM-5) for methane combustion. As a result, the PdO x species anchored by Brønsted acid sites of H-ZSM-5 exhibit high performance for catalytic combustion of CH 4 over Pd/H-ZSM-5 catalysts.
Upgrading olefin in the synthetic oil to alkane is highly desired due to its high volatility and ... more Upgrading olefin in the synthetic oil to alkane is highly desired due to its high volatility and thermal unstability as well as low energy density. Unlike conventional hydrotreating, methane (CH 4) was used in this study as the novel hydrogen donor for olefin saturation. The significant increase of H/C atomic ratio of product oil from 1.69 ± 0.02 (over pure ZSM-5) to 2.04 ± 0.02 (over Ir/ZSM-5 (10.0)) and the alkane content up to 83.8 ± 2.1% in the upgraded oil indicated that methane could exhibit comparable catalytic performance to what hydrogen (H 2) did for olefin (1-Decene) upgrading over the developed bifunctional catalysts with low Ir loadings. The HRTEM and XPS data revealed that the highly dispersed metallic Ir particles with average size of 1.32 nm was coexisting with IrO 2 species. The synergic effects of Ir/IrO 2 obviously promoted the activation of methane, which supplied sufficient hydrogen for the saturation and stabilization of olefin. The results from BET indicated that the pore size and volume of the ZSM-5 support were increased upon Ir introduction, which provided more active sites for cracking olefin (1-decene). NH 3-TPD results suggested that the presence of highly dispersed Ir increased the amount of surface acidity, which enhanced the formation and stabilization of carbenium ion intermediates. As a result, the produced alkanes were mainly composed of cyclopentane-derived compounds, like propylcyclopentane, 3-methylbutyl-cyclopentane and 1,2,4-trimethyl-cyclopentane, which has great application potential as immersion fluid and additive in the field of optics and petroleum.
Alkene can be converted to cycloalkane under methane environment over Pd/H-ZSM-5. Highly disperse... more Alkene can be converted to cycloalkane under methane environment over Pd/H-ZSM-5. Highly dispersed PdO x species benefits methane activation. Strength and amount of surface acidity play important role in olefin upgrading. Methane has potential to act as alternative hydrogen donor for olefin saturation. a b s t r a c t Olefin content minimization is critical for the long-term storage and long-distance transportation of oil product, which is commonly achieved through hydrogen saturation at high pressure to form paraffin. In this study, a novel catalytic process is reported to convert olefin to cycloalkane under methane environment with high selectivity. The main components of the product oil collected over Pd/ZSM-5 catalysts during olefin model compound (i.e., 1-decene) upgrading are cyclopentane, 1-methylbutyl-and cyclopentane, hexyl-while there are more than 46 species identified in the liquid product from the run with H-ZSM-5 support engaged. The total selectivity of the aforementioned cycloalkane products is up to 91.3% when 0.27 wt% Pd/ZSM-5 catalyst is charged, thus making the product oil more profitable. The HRTEM and XPS data reveal that the highly dispersed palladium particles are in the form of PdO x. The results from pyridine FT-IR and NH 3-TPD indicate that these PdO x species anchored onto the surface acidic sites exhibit the moderate acidic feature of Lewis acidic sites, which enhances the formation and stabilization of carbenium ion intermediates generated from 1-decene cracking. The strong interaction between PdO x species and surface acidic sites could not only stabilize the particle size and modify the electronic structure of Pd species but also modulate the acidic properties of ZSM-5 support, leading to promoted methane activation which would not only release sufficient hydrogen donors for preventing olefin aromatization, but also inhibit the over-cracking of carbenium ions. As a result, the selectivity of catalyst assisted olefin cyclization under methane environment is greatly enhanced.
A novel strategy is reported in this study to design a novel bifunctional PdO x /H-ZSM-5 catalyst... more A novel strategy is reported in this study to design a novel bifunctional PdO x /H-ZSM-5 catalyst for selective hy-drogenation of olefin. PdO x species (basic oxides) anchored on the strong acidic sites (Brönsted acid sites) of ze-olite support could not only generate new acidic sites with moderate acidic strength but also exhibit good capability for H 2 activation and dissociation. The conversion of 1-decene is 100% and total selectivity of methyl -nonane is 98.4 ± 0.4% at 350 °C. Our research might provide a valuable approach to design a highly efficient bifunctional catalyst for olefin upgrading.
ABSTRACT The doping of In2O3 significantly promoted the catalytic performance of Co3O4 for CO oxi... more ABSTRACT The doping of In2O3 significantly promoted the catalytic performance of Co3O4 for CO oxidation. The activities of In2O3–Co3O4 increased with an increase in In2O3 content, in the form of a volcano curve. Twenty-five wt % In2O3–Co3O4 (25 InCo) showed the highest CO oxidation activity, which could completely convert CO to CO2 at a temperature as low as −105 °C, whereas it was only −40 °C over pure Co3O4. The doping of In2O3 induced the expansion of the unit cell and structural distortion of Co3O4, which was confirmed by the slight elongation of the Co–O bond obtained from EXAFS data. The red shift of the UV–vis absorption illustrated that the electron transfer from O2– to Co3+/Co2+ became easier and implied that the bond strength of Co–O was weakened, which promoted the activation of oxygen. Low-temperature H2-TPR and O2-TPD results also revealed that In2O3–Co3O4 behaved with excellent redox ability. The XANES, XPS, XPS valence band, and FT-IR data exhibited that the CO adsorption strength became weaker due to the downshift of the d-band center, which correspondingly weakened the adsorption of CO2 and obviously inhibited the accumulation of surface carbonate species. In short, the doping of In2O3 induced the structural defects, modified the surface electronic structure, and promoted the redox ability of Co3O4, which tuned the adsorption strength of CO and oxygen activation simultaneously.Keywords: Co3O4; In2O3; CO oxidation; CO adsorption strength; redox ability; surface carbonate species
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