ON THE DEACTIVATION OF SUPPORTED PALLADIUM HYDROGENATION CATALYSTS BY THIOPHENE POISONING

The deactivation of supported palladium catalysts for ethylbenzene hydrogenation by thiophene was studied. The presence of Pd(n+) species on the catalyst surface, in samples prepared from acid solutions of PdCl2, and reduced at temperatures below 450-degrees-C, was evidenced by XPS. A correlation between the concentration of electron-deficient Pd species and the sulfur resistance was found. Thus, the higher the value of the Pd(n+)/Pd0) ratio, the higher the sulfur resistance. Catalysts prepared from Pd(NO3)2 or from PdCl2 reduced at 450-degrees-C, which essentially contain Pd0, are more quickly deactivated. Furthermore, our results also suggest that while the influence of the metal dispersion on the stability of the palladium catalysts toward sulfur is not significant, the nature of the support, on the other hand, plays an important role.