FTIR study of CO adsorption on coked Pt-Sn/Al2O3 catalysts

• Published in: Catalysis letters 1999-01, Vol.58 (4), p.189-194
• Main Authors: ARTEAGA, G. J, ANDERSON, J. A, ROCHESTER, C. H
• Format: Article
• Language: English
• Subjects: Adsorption; Aluminum oxide; Catalysis; Catalysts; Catalytic reactions; Chemistry; Coke; Coking; Coordination; Dilution; Exact sciences and technology; General and physical chemistry; Heat treatment; Heptanes; Infrared spectra; Oxidation; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Tin
• ISSN: 1011-372X; 1572-879X
• DOI: 10.1023/A:1019023210896

Infrared spectra of adsorbed CO have been used as a probe to monitor changes in Pt site character induced by the coking of Pt/Al2O3 and Pt–Sn/Al2O3 catalysts by heat treatment in heptane/hydrogen. Four distinguishable types of Pt site for the linear adsorption of CO on Pt/Al2O3 were poisoned to different extents showing the heterogeneity of the exposed Pt atoms. The lowest coordination Pt atoms (ν(CO) < 2030 cm−1) were unpoisoned whereas the highest coordination sites in large ensembles of Pt atoms (2080 cm−1) were highly poisoned, as were sites of intermediate coordination (2030–2060 cm−1). Sites in smaller two‐dimensional ensembles of Pt atoms (2060–2065 cm−1) were partially poisoned, as were sites for the adsorption of CO in a bridging configuration. The addition of Sn blocked the lowest coordination sites and destroyed large ensembles of Pt by a geometric dilution effect. The poisoning of other sites by coke was impeded by Sn, this effect being magnified for Cl‐containing catalyst. Oxidation or oxychlorination of coked catalyst at 823 K followed by reduction completely removed coke from the catalyst surfaces.