Influence of the alumina crystal phase on the performance of CoMo/Al2O3 catalysts for the selective hydrodesulfurization of fluid catalytic cracking naphtha

To achieve a high desulfurization degree while minimizing the olefin hydrogenation (HYD) is the biggest challenge in the selective hydrodesulfurization (HDS) of fluid catalytic cracking (FCC) naphtha. In this work, alumina with different crystal phases (gamma-Al2O3, delta-Al2O3 and theta-Al2O3) were utilized as carriers to prepare CoMo/Al2O3 selective HDS catalysts. The influence of alumina crystal phase on the morphology of active phase and catalytic performance of their corresponding CoMo/Al2O3 catalysts has been studied in detail. It was found that CoMo/delta-Al2O3 showed the highest HDS activity due to an appropriate weakened metal-support interaction and the modest Mo dispersion. However, CoMo/theta-Al2O3 showed a much higher HDS selectivity than that of CoMo/gamma-Al2O3 and CoMo/delta-Al2O3. The significantly enhanced HDS selectivity was attributed to a notably larger edge-to-corner ratio of CoMoS slabs (f(e)/f(c))(CoMo), thus resulting in a slightly reduction of HDS activity while a significantly decreased olefin HYD activity. Besides, the large pores of theta-Al2O3 are beneficial for weakening the internal diffusion resistance when utilizing full-size catalysts. Therefore, theta-Al2O3 is an ideal carrier to prepare the industrial CoMo/Al2O3 catalysts for the HDS of FCC naphtha.