Studies of molybdena-alumina catalysts: XVIII. Lanthanum-Modified supports

Abstract

A series of modified γ-alumina supports, to which 2–20% lanthanum was added, served as supports to prepare catalysts containing 6% Mo. The supports and catalysts were characterized, in the oxide and/or sulfide states, by XRD, ESCA, infrared spectroscopy, chernisorption Of CO 2, and catalytic activity for thiophene hydrodesulfurization and hexene hydrogenation. The results showed evidence for strong interaction between the alumina and the lanthana, the latter forming a monomolecular overlayer on the alumina surface. At high La content, some La underwent sulfiding. The Mo interacted with the La-OH groups during calcination, forming essentially monolayer slabs of Mo-sulfide after sulfiding. Catalytic activities slightly decreased then increased with La loading, the latter being more pronounced for hydrogenation. Correlation of activities with NO adsorption from infrared measurements were interpretated in terms of a support effect of La on the Mo-sulfide active sites.