We embedded Ru nanoparticles into mesoporous TiO2 submicrospheres (MTSSs) with tunable morphologies for benzene selective hydrogenation (BSH). It was identified that the TiO2 precursor prepared by the sol-gel step bore smooth microsphere morphology, which was transformed into the submicrosphere morphology with a rough surface by the subsequent solvothermal treatment and calcination, accompanied by a sharp increase in pore size but a decrease in acidity. The gradual elevation in the content of ammonia in the solvothermal mixture from 0 to 9.1 vol % further increased the pore size while imposing no evident impact on the acidity. In BSH to cyclohexene, the turnover frequency experienced the same variation as the acidity of the Ru@MTSS catalysts, whereas the initial selectivity toward cyclohexene (S-0) volcanically evolved with the pore size passing through a maximum of 90%, ascribed to the easy diffusion and desorption but suppressed readsorption of cyclohexene in the mesopores with proper size.