| Abstract
| - The influence of the Na+/H+ ratio on the benzene hydrogenation activity and the sulfur tolerance of Pt supportedon mordenite (MOR) was studied by in situ XANES. An increase of the Pt white line was observed withincreasing concentrations of thiophene up to 400 ppm, which indicates that an equilibrium exists between thethiophene concentration in the gas phase and the sulfur compounds present on the metal surface. Above acertain concentration of thiophene the Pt white line was constant, indicating a saturation of the metal surfacewith thiophene. The effect of sulfur poisoning on the metal surface was more effective for Pt supported onH-MOR compared to the more basic Pt/Na-MOR catalysts, which is attributed to the more pronounceddecomposition of thiophene and the formation of H2S on Brønsted acid sites. During benzene hydrogenation,a decrease of the Pt white line resulting from the adsorption of benzene and other reaction intermediates onthe Pt surface was observed. In the presence of sulfur, the increase of the Pt white line intensity duringbenzene hydrogenation suggests a higher sulfur coverage of the metal for Pt/H-MOR compared to Pt/NaH-MOR. An optimum concentration of acid sites was found with respect to the benzene hydrogenation rate andsulfur tolerance of the catalysts, which is attributed to the presence of two reaction pathways for benzenehydrogenation, i.e., one which is catalyzed by Pt and another in which acid sites close to Pt particles are thecatalitycally active sites.
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