Geometric and electronic effects in the conversion of methylcyclopentane on Pt-Sn catalysts

Abstract

With non-calcined bimetallic Pt—Sn/Al 2O 3 catalysts containing 1% Pt and 0.06 – 4% Sn, previous work has shown a complete reduction of tin for a content <1%. The properties of these catalysts were investigated for the conversions of methylcyclopentane (MCP), methylcyclopentene, hexane, cyclohexene and cyclohexane. A comparison of the product distribution clearly shows that the aromatisation of MCP follows a pure metallic route at temperatures lower than 673 K. Coke and sulphur deposition have effects similar to tin addition. The experimental evidence shows that for C-C bond rupture, the main role of tin is to dilute the platinum surface, as coke and sulphur do. Aromatisation goes through a maximum as a function of tin content. At high tin contents, the main reaction is dehydrogenation to methylcyclopentenes. Sulphur or coke does not affect aromatisation and dehydrogenation markedly. The special behaviour of tin is interpreted in terms of an electronic modification of platinum in the bimetallic catalyst.