Catalytic Functionalities of Supported Sulfides II. Effect of Support on MO Dispersion

Several MO and CoMo catalysts on different supports, previously evaluated for thiophene hydro-desulfurization (HDS) and I-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 AhO,, several Si01A1203 compositions, and SiOZ, it was found that essentially monolayer dispersion of the MO was present on AllO and low SiO*-containing supports, whereas in the case of high SiOz-containing and SiOZ 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 MO & phase present