AROMATICS REDUCTION OVER SUPPORTED PLATINUM CATALYSTS .1. EFFECT OF SULFUR ON THE CATALYST DEACTIVATION OF TETRALIN HYDROGENATION

The effects of sulfur on the deactivation of gamma-alumina-supported platinum catalysts for aromatics reduction were investigated. The catalytic test reactions were carried out in a continuous fixed-bed reactor at 270 degrees C and 180-480 pig. Both fresh and used catalysts were characterized by elemental analysis, fast Fourier transform infrared (FFT-IR) spectroscopy, temperature-programmed reduction (TPR), and electron probe microanalysis (EPMA). A Langmuir-Hinshelwood reaction model, which is based on a chemisorption scheme with irreversible surface reaction control for tetralin hydrogenation and reversible surface reaction for sulfur poisoning, was proposed to describe the deactivation kinetics. The kinetic results show that the reactivation rate constant decreases with the severity of sulfur poisoning, while the deactivation rate constant is comparatively unrelated. The TPR results are consistent with the catalytic performance test; a severely sulfur-poisoned catalyst needs to be reduced at higher temperature. FFT-IR spectroscopy characterizing CO adsorbed on the fresh and sulfur-poisoned catalysts indicated that the bond strength between CO and platinum was weakened with an increase of sulfur poisoning. EPMA spectroscopy characterizing the metal profiles of the catalysts indicated a metal migration during sulfur poisoning.