CATALYTIC PROPERTIES OF GAMMA-ALUMINA-SUPPORTED PT CATALYSTS FOR TETRALIN HYDROGENATION - EFFECTS OF SULFUR-POISONING AND HYDROGEN REACTIVATION

Tetralin hydrogenation was chosen as a model reaction for aromatics re duction reaction. The effects of sulfur-poisoning on the catalytic pro perties of gamma-alumina-supported Pt catalysts were investigated by k inetic studies carried out in a continuous fixed-bed reactor at 543 K, under 32 atm total pressure, and weight hourly space velocity (WHSV) ranging from 2.0 to 12 h(-1). An empirical power-law rate reaction was used to model the reaction kinetics. Parameter estimation results ind icated that both the reaction order and rate constant decreased with i ncreasing sulfur concentration; 500 ppm sulfur-poisoned catalysts were reactivated by hydrogen treatment at 723 and 823 K, respectively. The electronic properties of fresh, sulfur-poisoned, and hydrogen-reactiv ated catalysts were investigated by fast Fourier transform infrared (F T-IR) spectroscopy characterizing CO adsorbed on the catalysts. The re sults indicated that the bond strength between CO and platinum was wea kened with the increase of sulfur-poisoning, suggesting that the adsor ption of H2S and/or the formation of PtS decreased electronic density of Pt clusters. The electronic density can be regained by hydrogen rea ctivation, indicated by the results of FT-IR and X-ray absorption near -edge structures (XANES) spectroscopy. The decrease of reaction order with the severity of sulfur-poisoning may have resulted from the decre ase of electronic density of the Pt clusters and thus can be recovered with hydrogen reactivation. In contrast, the activity of the sulfur-p oisoned catalyst was not fully recovered because of the sulfur-poisoni ng induced Pt agglomeration and the residue sulfur deposited on Pt sit es, inferred from the EXAFS, FT-IR, and chemical analysis results. The comparison of the structure between the sulfur-poisoned and the hydro gen-reactivated catalysts indicates that the adsorbed H2S was removed at 723 K, while the morphology of the Pt clusters had no significant c hanges after the hydrogen treatment; hydrogen reactivation is unable t o redisperse the catalysts. (C) 1998 Academic Press.