Preparation and catalytic properties of chromium-containing mixed sulfides

A series of mixed sulfides dispersions MCr(2)S(4) (M = Mn, Fe, Co, Ni, Cu, Zn, Cd, 2Na) has been prepared by means of different chemical methods including sulfidation of mixed oxide dispersions or pyridinium dichromate complexes or reactions in the polysulfide-containing ionic fluxes. The solids were characterized using X-ray diffraction, BET surface measurements, X-ray photoelectron spectroscopy, low-energy ion scattering spectroscopy, and temperature programmed reduction. The catalytic properties of mixed sulfides were determined in the model reactions of tetraline hydrogenation and thiophene hydrodesulfurization. Variations of the specific activity of MCr(2)S(4) solids as a function of M in both reactions were similar, having the maxima for the NiCr(2)S(4) and CoCr(2)S(4) compounds. Differences in the catalytic activity were correlated with the reducibility, determined as the amount of sulfur removed from the catalysts by hydrogen at 573 K. The reducibility of MCr(2)S(4) solids follows from their electronic structure, as illustrated by the extended Huckel calculations. (C) 2000 Academic Press.