Dispersion and location of molybdenum sulfides supported on zeolite for hydrodesulfurization

The dispersion and location of zeolite-supported molybdenum sulfide species have been studied by means of XAFS, XPS, XRD, HREM and pore volume measurements. The zeolites used in the present study were NaY, USY and EMT. Molybdenum sulfide catalysts were prepared by Mo(CO)₆ adsorption and impregnation techniques, the former catalysts being considerably more active than the latter systems for the hydrodesulfurization of thiophene and hydrogenation of butadiene. It was demonstrated that with NaY-supported catalysts, molybdenum sulfide species derived from Mo(CO)₆ were completely sulfided and highly dispersed inside the zeolite pores. The crystal structure of the host zeolite was not destroyed by the accommodation of the molybdenum sulfide species in the pores. The relative activity of the catalyst for the hydrodesulfurization of substituted thiophenes and pore volumes measured using benzene as an adsorbate were in conformity with the HREM observations that the molybdenum sulfide clusters are located inside the zeolite pores. The structure and dispersion of the molybdenum sulfide species prepared using Mo(CO)₆ encaged in zeolite were shown to depend on the zeolite composition and crystal structure. Molybdenum sulfide species in the impregnation catalyst were found to be incompletely sulfided and poorly dispersed in contrast to the molybdenum sulfide catalysts prepared from Mo(CO)₆.