Chromia and chromium sulfide pillared clays differing in pillar density

Abstract

Chromia pillared clays differing in pillar density were synthesized from the Li-form of montmorillonite calcined in a controlled manner. These materials were characterized by XRD, TGA, AAS, nitrogen adsorption and their thiophene hydrodesulfurization activity. It is found that clays varying in cation exchange capacity pillared with Cr 12 pillar precursor ions can provide a family of catalysts that differ in surface area, porous structure and concentration of active sites. Sulfidation of the heat-treated chromia pillared clay resulted in the formation of chromium sulfide pillared derivatives with high surface area and well-developed porous structure. The activities for thiophene hydrodesulfurization and consecutive butene hydrogenation over chromium sulfide pillared montmorillonite are highest on clays with the largest pillar concentration and correlated with the total surface area. However, the activity per number of pillars increased with decreasing pillar density. Thiophene HDS predominantly results in the formation of butane and butenes, irrespective of the pillar population. The rate of deactivation is somewhat larger for catalysts that have a larger lateral pillar spacing. The chromium sulfide pillared clays exhibit a relatively high stability in thiophene HDS compared to zeolitic catalysts which is most likely due to their low protonic acidity.