MODELING OF SULFUR DEACTIVATION OF NAPHTHA-REFORMING CATALYSTS - STRUCTURE SENSITIVITY IN CYCLOPENTANE HYDROGENOLYSIS

The effect of particle size and the addition of Ir on the relative sul fur sensitivity of Pt-based catalysts has been studied. Cyclopentane h ydrogenolysis, a structure-sensitive reaction, was employed as a test reaction and thiophene as the poisoning molecule. Fresh and sintered m onometallic Pt/Al2O3 and bimetallic Pt-Ir/Al2O3 catalysts were used. S ulfur poisoning in the presence of simultaneous coke deactivation was characterised by two deactivation kinetic models. Model I assumes a si ngle deactivation order for both deactivation causes, whereas in model II different deactivation orders were assumed (d(c) = 1, d(s) = 0.5). Thioresistance, calculated from the above models as the number of sul fur atoms initially needed to deactivate one atom of exposed Pt, was i n the order: Pt-2 greater than or equal to Pt-1 > Pt-1A greater than o r equal to Pt-Ir greater than or equal to Pt-2A. According to the deac tivation models, thioresistance mainly depends on k(s), the specific r ate constant of hydrogenolysis of adsorbed thiophene. The higher the h ydrogenolytic constant, the lower the thioresistance. Moreover, both c yclopentane hydrogenolysis and sulfur poisoning depend on the mean par ticle size. When the particle size was increased, a higher hydrogenoly tic activity and a lower thioresistance were observed. Thus sulfur dea ctivation is also a structure-sensitive reaction.