Size and Shape Dependence on Pt Nanoparticles for the Methylcyclopentane/Hydrogen Ring Opening/Ring Enlargement Reaction S. Alayoglu • C. Aliaga • C. Sprung • G. A. Somorjai Received: 7 April 2011 / Accepted: 12 June 2011 / Published online: 23 June 2011 Ó Springer Science+Business Media, LLC 2011 Abstract Monodisperse Pt nanoparticles (NPs) with well-controlled sizes in the range between 1.5 and 10.8 nm, and shapes of octahedron, cube, truncated octahedron and spheres (*6 nm) were synthesized employing the polyol reduction strategy with polyvinylpyrrolidone (PVP) as the capping agent. We characterized the as-synthesized Pt nanoparticles using transmission electron microscopy (TEM), high resolution TEM, sum frequency generation vibrational spectroscopy (SFGVS) using ethylene/H 2 reaction as the surface probe, and the catalytic ethylene/H 2 reaction by means of measuring surface concentration of Pt. The nanoparticles were supported in mesoporous silica (SBA-15 or MCF-17), and their catalytic reactivity was evaluated for the methylcyclopentane (MCP)/H 2 ring opening/ring enlargement reaction using 10 torr MCP and 50 torr H 2 at temperatures between 160 and 300 °C. We found a strong correlation between the particle shape and the catalytic activity and product distribution for the MCP/ H 2 reaction on Pt. At temperatures below 240 °C, 6.3 nm Pt octahedra yielded hexane, 6.2 nm Pt truncated octahedra and 5.2 nm Pt spheres produced 2-methylpentane. In con- trast, 6.8 nm Pt cubes led to the formation of cracking products (i.e. C 1 –C 5 ) under similar conditions. We also detected a weak size dependence of the catalytic activity and selectivity for the MCP/H 2 reaction on Pt. 1.5 nm Pt particles produced 2-methylpentane for the whole temper- ature range studied and the larger Pt NPs produced mainly benzene at temperatures above 240 °C. Keywords Platinum Á Methylcyclopentane hydrogenation Á Ethylene/hydrogen probing by sum frequency generation vibrational spectroscopy Á Shape-controlled nanoparticles Á High-resolution electron microscopy Á Microscopy Á Spectroscopy and general characterisation Á Colloidal synthesis Á Preparation and materials 1 Introduction Selectivity is often of key importance to heterogeneous transformations of hydrocarbons [1], and thus achievable by controlling the size and/or shape of nanoparticle cata- lysts [2]. Structure-sensitive reactions such as pyrolle and furan hydrogenation on Pt [3–6], show strong dependence on particle size and/or shape. The hydrogenation of methylcyclopentane (MCP) is a multi-path and multi- product reaction, which yields C 6 isomers (i.e. hexane and its derivatives) via ring opening [1, 7–9], benzene via ring enlargement and dehydrogenation [10], and shorter chain hydrocarbons (i.e. C 1 –C 5 isomers) via cracking [11, 12]. Pt catalysts have been reported to be selective for the for- mation of branched hexane derivatives (i.e. 2-methylpen- tane and 3-methylpentane) [1, 13–16], however, no systematic study of the catalytic activity and product Electronic supplementary material The online version of this article (doi:10.1007/s10562-011-0647-6) contains supplementary material, which is available to authorized users. S. Alayoglu Á C. Aliaga Á C. Sprung Á G. A. Somorjai (&) Department of Chemistry, University of California, Berkeley, CA, USA e-mail: somorjai@berkeley.edu S. Alayoglu Á C. Aliaga Á C. Sprung Á G. A. Somorjai Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA Present Address: C. Sprung Department of Chemistry, SMN, University of Oslo, P.O. Box 1033, 0314 Oslo, Norway 123 Catal Lett (2011) 141:914–924 DOI 10.1007/s10562-011-0647-6