Catalytic functionalities of supported sulfides II. Effect of support on Mo dispersion

Abstract

Several Mo and CoMo catalysts on different supports, previously evaluated for thiophene hydrodesulfurization (HDS) and 1-hexene hydrogenation (HYD) activities, were characterized for Mo dispersion in the catalysts. Techniques employed for characterization included XRD, ESCA, and O2 chemisorption of catalysts, and determination of “active OH” on supports. For the calcined (oxide) form of Mo and CoMo catalysts on Al2O3, several SiO2---Al2O3 compositions, and SiO2, it was found that essentially monolayer dispersion of the Mo was present on Al2O3 and low SiO3-containing supports, whereas in the case of high SiO2-containing and SiO2 supports evidence was found for three-dimensional crystallites for the Mo phase. The sulfided form of these catalysts gave essentially the same results. These findings are interpreted in terms of the degree of interaction of the Mo phase with the support. To account for changes in HDS and HYD activities of the catalysts, it is proposed that HDS occurs at vacancies on corner sites and HYD at vacancies on edge sites of the MoS2 phase present.