Pollen-structured hierarchically meso/macroporous silica spheres (PHMSs) are synthesized using rape pollen grains 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 626 m(2) g(-1) and uniform mesopores with average pore size below 5 nm. With the Au content fixed at 6.8 wt%, the Au nanoparticles supported on the PHMSs achieved a higher CO conversion at an ambient temperature (30 degrees C) than those supported on typical mesoporous silica SBA-15. Au nanoparticles supported on PHMSs also reached 100% CO conversion at a lower temperature than those supported on the SBA-15. The effects of silica support on the catalytic performances are investigated through calculation of the diffusion coefficients and simulation of gas diffusion in PHMSs and SBA-15. It is shown that the hierarchical PHMSs facilitate gas diffusion better than the non-hierarchical SBA-15, hence leading to higher CO oxidation catalytic performance. (C) 2017 Elsevier Ltd. All rights reserved.