CO self-poisoning and slow surface kinetics pose major challenges to a CO oxidation catalyst that should work at ambient temperature.Furthermore,the presence of moisture would cause passivation of the catalyst A highl...CO self-poisoning and slow surface kinetics pose major challenges to a CO oxidation catalyst that should work at ambient temperature.Furthermore,the presence of moisture would cause passivation of the catalyst A highly active ceria promoted Pt catalyst（4%Pt-12%CeO_2/SiO_2;conversion≥99%at low（ 500 ppm） and high（ 2500 ppm） CO concentrations was developed for CO oxidation at ambient temperature in humid air.Catalyst preparation variables such as Pt and CeO_2 loading,ceria deposition method,drying and calcination conditions for the ceria and Pt precursors were optimized experimentally.The activity was correlated with surface properties using CO/H_2 chemisorption,O_2-H_2 titration,X-ray diffraction and BET surface area analysis.The method of CeO_2 deposition had a significant impact on the catalytic activity.CeO_2 deposition by impregnation resulted in a catalyst that was three times more active than that prepared by deposition precipitation or CeO_2grafting.O_2-H_2 titration results revealed that the close association of ceria and Pt in the case of CeO_2deposition by impregnation resulted in higher activity.The catalyst support used was also crucial as a silica supported catalyst was five times more active than an alumina supported catalyst.The particle size and pore structure of the catalyst support were also crucial as the reaction was diffusion controlled.The drying and calcination conditions of the ceria and Pt precursors also played a crucial role in determining the catalytic activity.The Pt-CeO_2/SiO_2 catalysts with Pt 2.5 wt%and CeO_2 15 wt%were highly active（TOF 0.02 s^（-1）） and stable（conversion 99%after 15 h） at ambient conditions.展开更多
Two-dimensional plain-weave silicon carbide fiber fabric reinforced silicon carbide(2D-SiC/SiC)composites were molded by stacking method and densified through precursor infiltration and pyrolysis(PIP)process.SiC coati...Two-dimensional plain-weave silicon carbide fiber fabric reinforced silicon carbide(2D-SiC/SiC)composites were molded by stacking method and densified through precursor infiltration and pyrolysis(PIP)process.SiC coating was deposited as the fiber/matrix interphase layer by chemical vapor deposition(CVD)technique.Fiber/matrix debonding and relatively long fiber pullouts were observed on the fracture surfaces.Additionally,the flexural strength and elastic modulus of the composites with and without fiber/matrix interphase layer were investigated using three-point bending test and single-edge notched beam test.The results show that the fiber fraction and the porosity of 2D-SiC/SiC composites with and without coating are 27.2%(volume fraction)and 11.1%,and 40.7%(volume fraction)and 7.5%,respectively.And the flexural strength and elastic modulus of 2D-SiC/SiC composites with and without coating are 363.3 MPa and 127.8 GPa,and 180.2 MPa and 97.2 GPa,respectively.With a proper thickness,the coating can effectively adjust the fiber/matrix interface,thus causing a dramatic increase in the mechanical properties of the composites.展开更多
Several TAAFS （tetraalkylammonium hexafluorosilicates） with different cations were synthesized. Their thermal properties were studied showing that obtained complexes are stable enough to be suitable for electrochemi...Several TAAFS （tetraalkylammonium hexafluorosilicates） with different cations were synthesized. Their thermal properties were studied showing that obtained complexes are stable enough to be suitable for electrochemical deposition of silicon coatings under temperatures at least up to 200 ℃.展开更多
基金supported by US Army contract(W56HZV-05-C0686) at Auburn University administered through TARDEC
文摘CO self-poisoning and slow surface kinetics pose major challenges to a CO oxidation catalyst that should work at ambient temperature.Furthermore,the presence of moisture would cause passivation of the catalyst A highly active ceria promoted Pt catalyst（4%Pt-12%CeO_2/SiO_2;conversion≥99%at low（ 500 ppm） and high（ 2500 ppm） CO concentrations was developed for CO oxidation at ambient temperature in humid air.Catalyst preparation variables such as Pt and CeO_2 loading,ceria deposition method,drying and calcination conditions for the ceria and Pt precursors were optimized experimentally.The activity was correlated with surface properties using CO/H_2 chemisorption,O_2-H_2 titration,X-ray diffraction and BET surface area analysis.The method of CeO_2 deposition had a significant impact on the catalytic activity.CeO_2 deposition by impregnation resulted in a catalyst that was three times more active than that prepared by deposition precipitation or CeO_2grafting.O_2-H_2 titration results revealed that the close association of ceria and Pt in the case of CeO_2deposition by impregnation resulted in higher activity.The catalyst support used was also crucial as a silica supported catalyst was five times more active than an alumina supported catalyst.The particle size and pore structure of the catalyst support were also crucial as the reaction was diffusion controlled.The drying and calcination conditions of the ceria and Pt precursors also played a crucial role in determining the catalytic activity.The Pt-CeO_2/SiO_2 catalysts with Pt 2.5 wt%and CeO_2 15 wt%were highly active（TOF 0.02 s^（-1）） and stable（conversion 99%after 15 h） at ambient conditions.
基金Project(NCET-07-0228)support by the New Century Excellent Talents in University
文摘Two-dimensional plain-weave silicon carbide fiber fabric reinforced silicon carbide(2D-SiC/SiC)composites were molded by stacking method and densified through precursor infiltration and pyrolysis(PIP)process.SiC coating was deposited as the fiber/matrix interphase layer by chemical vapor deposition(CVD)technique.Fiber/matrix debonding and relatively long fiber pullouts were observed on the fracture surfaces.Additionally,the flexural strength and elastic modulus of the composites with and without fiber/matrix interphase layer were investigated using three-point bending test and single-edge notched beam test.The results show that the fiber fraction and the porosity of 2D-SiC/SiC composites with and without coating are 27.2%(volume fraction)and 11.1%,and 40.7%(volume fraction)and 7.5%,respectively.And the flexural strength and elastic modulus of 2D-SiC/SiC composites with and without coating are 363.3 MPa and 127.8 GPa,and 180.2 MPa and 97.2 GPa,respectively.With a proper thickness,the coating can effectively adjust the fiber/matrix interface,thus causing a dramatic increase in the mechanical properties of the composites.
文摘Several TAAFS （tetraalkylammonium hexafluorosilicates） with different cations were synthesized. Their thermal properties were studied showing that obtained complexes are stable enough to be suitable for electrochemical deposition of silicon coatings under temperatures at least up to 200 ℃.
