CoMo/Al2O3 catalysts prepared by tailoring the surface properties of alumina for highly selective hydrodesulfurization of FCC gasoline

Abstract

Traditionally prepared CoMo/Al2O3 hydrotreating catalysts, although efficient for deep desulfurization, are not suitable for fluid catalytic cracking (FCC) gasoline hydrodesulfurization (HDS) due to their high olefin hydrogenation (HYD) activity especially when the HDS conversion is high. Herein, two alumina supports with tailored surface properties were prepared by calcination of hydrothermally treated pseudo-boehmite (PB) and hydrothermally treated γ-Al2O3 in order to design CoMo/Al2O3 catalysts with high HDS selectivity. It is found that compared with the traditional alumina prepared by direct calcination of PB, the two tailored alumina supports have notably decreased surface area, surface hydroxyl groups and Lewis acidity. The characterization results show that the catalysts obtained from CoMo supported on the two tailored supports have lowered Mo dispersion, weakened metal-support interaction, increased Mo sulfidation degree and longer MoS2 slabs than the traditional CoMo/Al2O3 catalyst. The catalytic results of three different CoMo/Al2O3 catalysts in the HDS of a full-range FCC gasoline show that the HDS selectivity is increased remarkably (selectivity factors increase from 5.5 to 11.0) with the decreased surface area, surface hydroxyl groups and Lewis acidity of the alumina supports. Especially, CoMo supported on the tailored alumina support prepared by calcination of hydrothermally treated γ-Al2O3 (denoted as CoMo/Al2O3-3) exhibits a 15% lower olefin HYD activity than traditional CoMo/Al2O3 catalyst even at the same and high HDS conversion (95%). The greatly improved HDS selectivity can be well explained by the increased slab length of supported MoS2 particles, resulting in notably decreased HYD activity catalyzed by the corner sites. Besides, CoMo/Al2O3-3 also shows superior HDS selectivity in the HDS of a real heavy FCC naphtha, where the sulfur content can be reduced from 309 ppm to 10 ppm with an accompanying RON loss of only 1.0 unit.