The importance of ultradeep hydrodesulfurization (HDS) of the cracked and straight run gasoil blend necessitate an extensive study on HDS catalyst optimization. Herein, we report a CO2 assisted neutralization of NaAlO2 aqueous solution conducted in a semibatch membrane dispersion microstructured reactor, as a novel method to synthesize pseudoboehmite powders with different textural properties. A number of gamma-Al2O3 catalyst supports as well as NiMo catalysts with the average pore sizes of 6.3 (5.2) to 21.5 (18.6) nm and 5.0 (3.7) to 20.3 (17.2) nm are prepared using the as synthesized pseudoboehmite powders. XRD analysis shows the sizes of all pseudoboehmite and gamma-Al2O3 supports crystalline are in the nanoscale range. NH3 TPD results reveal that about half of the total NH3 (1.76 mmol NH3/g) is adsorbed on the surface of gamma-Al2O3 support due to presence of strong acidic cites. FTIR spectrometer confirms formation of MoO4-2 species. The effects of catalyst pore size on HDS performance of the straight run gasoil and its blend with cracked gasoil are also investigated according which, the most sulfur removal from both feedstocks using catalysts with the average pore size of 8.0 (5.9) and 9.1 (7.2) nm, respectively, emphasizing the significant role of the pore size on the catalyst activity and HDS process efficiency. However, effects of textural and physicochemical properties of the catalyst and its support cannot be neglected. The obtained results confirm the proposed synthesis route would be an efficient alternative method to prepare mesoporous gamma-Al2O3 supports with precisely controlled average pore size in a wide range of a few up to 20 nm.