Chromia- and chromium sulfide-pillared clays : preparation, characterization, and catalytic activity for thiophene hydrodesulfurization

Chromia-pillared clay has been synthesized from naturally occurring montmorillonite through exchange of interlamellar ions with hydroxychromium polycations. Sulfidation of the heat-treated precursor with an H2S–H2mixture at 673 K results in the formation of chromium sulfide-pillared clay. The materials were characterized by X-ray diffraction, thermogravimetric analysis, nitrogen adsorption, scanning electron microscopy, electron probe microanalysis, and X-ray photoelectron spectroscopy. These methods showed that heat treatment of chromia-pillared clay under the conditions applied did not drastically change the pore structure or the chromium oxidation state and the distribution of pillars, but strongly influenced its aggregate morphology. Sulfide-pillared material has an interlamellar distance of 1.01 nm, a BET surface area of 256 m2g-1, a micropore volume of 0.082 cm3g-1, and a pore slitwidth of 1.24 nm. The sulfidation procedure does not significantly change the pillared structure or the chromium oxidation state. Sulfur is found to be present as practically uniformly distributed S2-species. The chromium sulfide phase in the finely dispersed and well-distributed state that is reached in sulfide-pillared clay is of primary importance to the high thiophene conversion over this catalyst. In the presence of this catalyst, thiophene hydrodesulfurization results exclusively in the formation of butane and butene. The distribution of hydrocarbons depends on the reaction temperature, with a higher butane yield at lower temperature