Isomerization of n -Hexane Catalyzed by Supported Monodisperse PtRh Bimetallic Nanoparticles
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Isomerization of n-Hexane Catalyzed by Supported Monodisperse PtRh Bimetallic Nanoparticles Nathan Musselwhite • Selim Alayoglu • Ge´roˆme Melaet Vladimir V. Pushkarev • Avery E. Lindeman • Kwangjin An • Gabor A. Somorjai
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Received: 28 May 2013 / Accepted: 3 July 2013 / Published online: 6 August 2013 Ó Springer Science+Business Media New York 2013
Abstract Composition and size of PtxRh1-x bimetallic nanoparticles were varied in order to study the effects in the catalytic reforming of n-hexane. Hexane isomerization, an analogue to the important industrial process of hydrocarbon reforming is a reaction in which we aim to investigate the molecular level details of catalysis. It is known, that in hydrocarbon isomerization, Pt atoms act to isomerize the reactants, while small amounts of ‘‘promoter metal’’ atoms (such as Rh, Ir, Re and Sn) provide C–C and C–H bond breaking activity. Herein, we report on the effect of composition and size in model bimetallic PtxRh1-x nanoparticle catalysts utilized in n-hexane reforming. Both nanoparticle composition and size were shown to influence catalytic turnover frequency and product selectivity. It was found, through ambient pressure X-ray photoelectron spectroscopy, that the surface of these nanoparticles is both dynamic, and Rh rich under relevant reaction conditions. The findings suggest that an ensemble effect exists, in which the highest isomer production occurs when Rh atoms are surrounded by Pt atoms on the metal surface.
Electronic supplementary material The online version of this article (doi:10.1007/s10562-013-1068-5) contains supplementary material, which is available to authorized users. N. Musselwhite S. Alayoglu G. Melaet A. E. Lindeman K. An G. A. Somorjai (&) Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA e-mail: [email protected] N. Musselwhite S. Alayoglu G. Melaet V. V. Pushkarev A. E. Lindeman G. A. Somorjai Chemical Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, USA
Keywords Reforming Heterogeneous catalysis Hexane isomerization PtRh bimetallic Ensemble effect Size effect
1 Introduction The catalytic reforming of n-hexane, a model reaction for naptha reforming, is an industrially important multi-product reaction. The goal of studying this reaction, along with any heterogeneous catalysis reaction is to simultaneously optimize catalytic activity and selectivity [1–3]. Hydrocarbon reforming is normally accomplished through the use of a platinum catalyst, alloyed with small amounts of other ‘‘promoter’’ metals and supported on an acidic support [4]. The promoter metals in this catalyst, which are typically middle transition metals with high C–C bond breaking activity, act to increase the overall activity of the reaction. Through the use of colloidal synthesis, monodisperse, composition controlled nanoparticles can be synthesized, characterized, and evaluated catalytically at industrially relevant conditions, which can help elucidate the i
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