Sulfur Resistance of Pt-W catalyst

Abstract

The sulfur resistance of low-loaded monometallic Pt catalysts and bimetallic Pt-W catalysts during the partial selective hydrogenation of styrene, a model compound of PYGAS streams, was studied. The effect of metal impregnation sequence on the activity and selectivity was also evaluated. Catalysts were characterized by ICP, TPR, XRD and XPS techniques. Catalytic tests with sulfur-free and sulfur-doped feeds were performed.All catalysts showed high selectivities (> 98%) to ethylbenzene. Activity differences between the catalysts were mainly attributed to electronic effects due to the presence of different electron-rich species of Pt0, and electron-deficient species of Ptä+. Pt0 promotes the cleavage of H2 while Ptä+ the adsorption of styrene. The catalyst successively impregnated with W and Pt (WPt/Al) was more active and sulfur resistant than the catalyst prepared with an inverse impregnation order (PtW/Al). The higher poison resistance of WPt/Al was attributed to the presence of chloride that inhibits the adsorption of thiophene because of steric and electronic effects. On the other hand, the lower concentration of chloride and a high concentration of Pt0 electron-rich sites (with low BE values) could contribute to the poisoning, as these species would act as electron donor sites, providing available electrons to be bond with the S atom of thiophene. Both effects would promote a strong adsorption of thiophene and thus an enhanced blocking of the catalyst active sites.