Applied Catalysis Ar General, 101 (1993) 185-198 Elsevier Science Publishers B.V., Amsterdam 185 APCAT A2551 Coking kinetics of fresh and thermally aged commercial Cr,O,/Al,O, catalyst” zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH J.A. Peiia, A. Mom&n and J. Santamaria Departamento de Ingetzieria Quimica y Tecnologias de1 Media Ambiente, Facultad de Ciencias, University of Zaragoza, 50.009 Zaragoza (Spain) and J.L.G. Fierro Instifuto de Catcilisisy Petroleoquimica de1 CSIC, Campus UAM, Cantoblanco 28.049 Madrid (Spain) (Received 23 December 1992, revised manuscript received zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR 14 April 1993) zyxwvutsrqponmlkjihgfedcb Abstract The coking behaviour of fresh and of thermally aged Cr,O:,/Al,O:, catalysts has been studied during the dehydrogenation of n-butene to butadiene using a thermogravimetric system. The results show that catalyst aging decreases considerably the rate of the main reaction, but also the rate of coking. As a consequence, the dehydrogenation rates obtained after a certain reaction time with aged catalyst were higher than those for fresh catalyst. The analysis of the coking kinetics on fresh and on thermally aged catalyst and the X-ray photoelectron spectroscopy results obtained on both samples suggest that the deactivation mechanism is not changed by the aging process, and that the main effect of aging is to reduce the number of sites available on the surface for the main and coking reactions. Key words: aging; chromia/alumina; coking; deactivation; kinetics INTRODUCTION Virtually all catalysts lose their activity with time-on-stream. This makes catalyst regeneration or substitution necessary when the activity and/or selec- tivity reach a certain level which is considered the minimum for economical industrial operation. Obviously, the cause of deactivation determines to a large extent the method of regeneration. When catalyst coking is the cause, the activity may be restored Correspondence to: Dr. J. Santamaria, Departamento de Ingenieria Quimica y Tecnologias de1 Medio Ambiente, Facultad de Ciencias, IJniversity of Zaragoza, 50.009 Zaragoza, Spain. Tel. ( +34- 76) 353631, fax. (+34-76) 567920. “Paper presented at the XIII Iberoamerican Symposium, Segovia (Spain), 6- 10 July 1992. 6926-860X/93/$06.00 0 1993 Elsevier Science Publishers B.V. All rights reserved