Synthesis Of Three Dimentional Hierarchically Porous Au/SiO₂ Catalysts And Study On Their Performance Of CO Catalytic Oxidation

This paper inveatigate the structure effects of supports on CO catalysis by synthesizing three-dimentional hierarchically porous Au/SiO₂ catalysts with different structure.First,pollen-structured hierarchically meso/macroporous silica spheres（PHMSs）are synthesized using rape pollen grains with open connected net-like structure and a triblock copolymer（poly（ethylene oxide-block-propylene oxide-block-ethylene oxide）,P123）as templates.The PHMSs are comprised of mesoporous walls that form a macroporous structure replicating the net-like morphology of the pollen grain exine.The unique structure has a high BET surface area of 626m²·g^-1,total pore volume of 1.07cm³·g^-1,and uniform mesopores with average pore size of 3.6 nm.By loading Au nanoparticles on PHMSs,A nonel 3D hierarchically porous Au/SiO₂ catalyst—Au/PHMSs is obtained.The characterization and analysis of catalyst support and Au nanoparticles show that supported Au nanoparticles are relatively small（2⁵ nm）,with uniform distribution,highly crystallization and thermolstability.The CO catalytic oxidation tests are conducted to investigate the CO catalytic properties of Au/PHMSs catalysts.In the temperature range of 25⁷00°C,CO catalytic activity of Au/PHMSs increases with the Au loading content.With the Au content fixed at 6.8 wt%,hierarchical Au/PHMSs achieved a higher CO conversion than non-hierarchical Au/SBA-15 in the temperature range of 25⁵00°C.Compared with typical mesopores in Au/SBA-15,this advanced catalytic property of Au/PHMSs is due to positive effects of their meso/macroporous structure,which improves the mass transport.In order to further investigate the structure effects of supports and the mass transport phenomenon in CO catalysis reaction,hierarchical and non-hierarchical silica catalysts are used to calculate the diffusion coefficients and build models to simulate gas diffusion in Au/PHMSs and Au/SBA-15,which confirm that the hierarchical PHMSs facilitate gas diffusion better than the non-hierarchical SBA-15,hence leading to higher CO oxidation catalytic performance.According to this research idea,another three-dimentional hierarchically porous Au/SiO₂ catalyst—three-dimentional ordered arrays of multilamellar silica nanoparticles with Au nanoparticles（Au/MLSs）is also built to study its CO catalysis activity,which shows that hierarchical Au/MLSs achieved a higher CO conversion than non-hierarchical Au/SBA-15.With this three-dimentional ordered hierarchically structure,catalyst models are constructed to study the ordering effects of supports.The calculation and simulation results from which both show improved gas diffusion efficiency in hierarchical Au/MLSs catalysts and the structure effects of supports on improving CO catalysis efficiency is further demonstrated.Therefore this paper not only provides a new method for investigating the structure effects of silica supported Au nanoparticles catalysts,but also inspires the design of novel CO catalsts in the future.