Influence of chlorine on the catalytic properties of supported rhodium, iridium and platinum in ring opening of naphthenes

Authors:  P. Samoila, F. Epron, P. Marécot, C. Especel

Abstract:
Pt, Ir and Rh were deposited on SiO₂ or Al₂O₃ using chlorinated precursors and various amounts of HCl in the impregnation medium. The Brønsted and Lewis acidities increased with the chlorine content of the alumina supported catalysts. The silica-supported catalysts only presented Lewis acid sites. The catalysts were evaluated in methylcyclopentane (MCP) and methylcyclohexane (MCH) ring-opening (RO) under pressure (2.85 and 3.95 MPa, respectively), from 200 to 425^◦C. For MCP conversion, the acidity of the alumina support had no sensitive effect on the activity and selectivity to RO products, and few effects on the distribution of RO products. No isomerization or hydrocracking products were observed, confirming that these reactions occurred mainly on the metal function, which was not modified by the presence of chlorine. The nature of the support, SiO₂ or Al2O3, had a strong effect on both the activity (1.9 against 0.5 mol h−1 g−1 metal for Ir/Al₂O₃ and Ir/SiO₂, respectively at 225 ◦C) and selectivity to RO products (99.6% against 97.5% for Ir/Al₂O₃ and Ir/SiO₂, respectively, at 80% of MCP conversion) for Ir catalysts only. Interestingly, the Rh/SiO₂ exhibited a high selectivity for converting MCP to RO products, similar to Ir/Al₂O₃, i.e. 99.6% at 80% of conversion. Depending on the metal and the supports, three types of behavior were observed for MCH ring-opening: (i) a direct ring-opening on the metal function whatever the support for Ir, (ii) a first step of isomerization, and then a need of a sufficiently acidic support, for Pt and (iii) an intermediate behavior for Rh, which was able to either directly convert MCH in absence of acidic support or favor a bifunctional mechanism on chlorinated alumina.

Keywords:
Ring-opening
Ir
Pt
Rh
Methylcyclopentane
Methylcyclohexane
Chlorine

Published in: Applied catalysis A: General  (Volumes 462–463, Pages 1-310, 10 July 2013)

Publisher: Elsevier      

ISSN Information: 0926-860X

Influence of chlorine on the catalytic properties of supported rhodium, iridium and platinum in ring opening of naphthenes

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