CHROMIA-PILLARED AND CHROMIUM-SULFIDE-PILLARED CLAYS - PREPARATION, CHARACTERIZATION, AND CATALYTIC ACTIVITY FOR THIOPHENE HYDRODESULFURIZATION

Chromia-pillared clay has been synthesized from naturally occurring mo ntmorillonite through exchange of interlamellar ions with hydroxychrom ium polycations. Sulfidation of the heat-treated precursor with an H2S -H-2 mixture at 673 K results in the formation of chromium sulfide-pil lared clay. The materials were characterized by X-ray diffraction, the rmogravimetric analysis, nitrogen adsorption, scanning electron micros copy, electron probe microanalysis, and X-ray photoelectron spectrosco py. These methods showed that heat treatment of chromia-pillared clay under the conditions applied did not drastically change the pore struc ture or the chromium oxidation state and the distribution of pillars, but strongly influenced its aggregate morphology. Sulfide-pillared mat erial has an interlamellar distance of 1.01 nm, a BET surface area of 256 m(2) g(-1), a micropore volume of 0.082 cm(3) g(-1), and a pore sl itwidth of 1.24 nm. The sulfidation procedure does not significantly c hange the pillared structure or the chromium oxidation state. Sulfur i s found to be present as practically uniformly distributed S2- species . The chromium sulfide phase in the finely dispersed and well-distribu ted state that is reached in sulfide-pillared clay is to the high thio phene conversion over this catalyst. In the presence of this catalyst, thiophene hydrodesulfurization results exclusively in the formation o f butane and butene. The distribution of hydrocarbons depends on the r eaction temperature, with a higher butane yield at lower temperature. (C) 1997 Academic Press.