TEMPERATURE-PROGRAMMED REDUCTION AND HDS ACTIVITY OF SULFIDED TRANSITION-METAL CATALYSTS - FORMATION OF NONSTOICHIOMETRIC SULFUR

Citation
Pj. Mangnus et al., TEMPERATURE-PROGRAMMED REDUCTION AND HDS ACTIVITY OF SULFIDED TRANSITION-METAL CATALYSTS - FORMATION OF NONSTOICHIOMETRIC SULFUR, Journal of catalysis, 151(1), 1995, pp. 178-191
Citations number
26
Categorie Soggetti
Chemistry Physical
Journal title
ISSN journal
00219517
Volume
151
Issue
1
Year of publication
1995
Pages
178 - 191
Database
ISI
SICI code
0021-9517(1995)151:1<178:TRAHAO>2.0.ZU;2-2
Abstract
Sulfided alumina-supported transition metal catalysts have been studie d using temperature-programmed reduction (TPR). The H-2 and H2S concen trations were determined simultaneously and the major processes occurr ing were discriminated, namely reduction of oxidic and sulfidic specie s and desorption of H2S. Because of the high maximum reduction tempera ture and the high hydrogen partial pressure applied, a complete descri ption of all species was acquired, except for the Cr and Mn catalysts which could not be reduced below 1270 K. After sulfiding at 673 K, TPR of alumina-supported transition metals showed that several types of s ulfur were present, viz. (i) sulfur species with a stoichiometry in ag reement with bulk thermodynamics, indicated as stoichiometric sulfur, (ii) a nonstoichiometric sulfur species (S-x) which was present in exc ess of the S/Me ratio based on bulk thermodynamics (not identical to e lemental sulfur since it is present after purging at 673 K), (iii) S-H groups, and (iv) adsorbed H2S. The mechanism of S-x formation is disc ussed. The amounts of nonstoichiometric sulfur mainly depended on the type of transition metal and the pretreatment procedure. The influence of the reductibility of the stoichiometric and nonstoichiometric sulf ur species on the hydrodesulfurisation activity is discussed. The resu lts presented indicate that chemisorption measurements may depend on t he pretreatment of sulfided catalysts. (C) 1995 Academic Press, Inc.