A series of mesoporous sieves with different pore diameters and structures have been controllably synthesized by adding variable amounts of swelling agent 1,3,5-trimethylbenzene in the preparation process for SBA-15. NiMo catalysts supported by mesoporous sieves are prepared by using the newly proposed Mo-based organic-inorganic hybrid nanocrystals as precursors to load Mo and subsequently using wetness impregnation to load Ni. The hydrodesulfurization (HDS) activity of these obtained catalysts is evaluated in a continuously flowing tubular fixed-bed microreactor using 1 wt% dibenzothiophene (DM.) in heptane as a model compound. The results show that HDS ratio has gradually increased as the pore diameter of supports is enlarged from 7 to 11 nm with the mesostructure keeping an ordered two-dimensional hexagonal symmetcy. When the structure is in the intermediate stage of structural transition from ordered hexagonal mesostructure to mesocecullar structure, HDS ratio is decreased dramatically due to the disordered and collapsed structure to block the pore channels. After the mesocecullar structure with three-dimensional open pore channels is formed which is more convenient for the molecular diffusion, HDS ratio has increased again as a result It is concluded that both the pore size and window size connecting the adjacent pores play an important role in the HDS activity but the window size is of more significant importance, which is the key point for the enhanced catalytic performance. (c) 2014 Elsevier Ltd. All rights reserved,