Selective ring opening of methylcyclopentane over Pt/γ-Al2O3, Ir/γ-Al2O3 and Pt-Ir/γ-Al2O3 catalysts with hydrogen at atmospheric pressure

摘要

Pt/γ-Al2O3, Ir/γ-Al2O3 and Pt-Ir/γ-Al2O3 were prepared by incipient wetness impregnation and co-impregnation methods. The catalysts were characterised by the classical physico-chemical techniques of SEM, TEM, XRD, N2-sorption, H2-TPR and elemental analysis. The metallic particles were highly dispersed on the support, assuming the presence of an icosahedral Mackay structure, which is a limited only by (111) face. The performances of the catalysts were investigated in the conversion of methylcyclopentane (MCP) with hydrogen at atmospheric pressure at temperatures between 180 and 400 °C. At low temperature, only Ir/γ-Al2O3 showed the ability to open MCP with an atom economy (S_(RO) = 100%) and without by-products from cracking and ring enlargement reactions. Ir/γ-Al2O3 opened the MCP ring at the secondary-secondary positions. The Pt/γ-Al2O3 and Pt-Ir/γ-Al2O3 catalysts opened MCP starting at 220 °C, in the secondary-tertiary positions, with atom economy (S_(RO) = 100%). The synergistic effect between Ir and Pt was observed in our conditions, but the Pt and Ir particles existed also as individual entities on the support. At high temperature, all the catalysts were inactive in MCP ring opening. Cracking reactions became more pronounced with increasing temperature and parallel decreases in ring opening selectivities. The formation of benzene was observed at high temperatures only on Pt/γ-Al2O3.