Reactivity of Ga 2 O 3 Clusters on Zeolite ZSM-5 for the Conversion of Methanol to Aromatics
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ORIGINAL ARTICLES
Reactivity of Ga2O3 Clusters on Zeolite ZSM-5 for the Conversion of Methanol to Aromatics Jose A. Lopez-Sanchez • Marco Conte • Phil Landon • Wu Zhou Jonathan K. Bartley • Stuart H. Taylor • Albert F. Carley • Christopher J. Kiely • Karim Khalid • Graham J. Hutchings
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Received: 10 May 2012 / Accepted: 28 June 2012 / Published online: 18 July 2012 Ó Springer Science+Business Media, LLC 2012
Abstract Composites of Ga2O3 clusters and zeolite ZSM-5 were evaluated for the transformation of methanol to hydrocarbons. Comparison of the activity with ZSM-5 showed that the Ga2O3 clusters are responsible for the enhanced selectivity to aromatics via contact synergy, thus showing the importance of non framework gallium species for this reaction. TEM analysis of fresh and spent catalysts allowed the identification of the formation of carbonaceous products at the Ga2O3/zeolite interface region, and this interface is also the probable location of the catalyst active sites. Keywords Aromatics
Gallium oxide ZSM-5 Methanol
J. A. Lopez-Sanchez M. Conte P. Landon J. K. Bartley S. H. Taylor A. F. Carley G. J. Hutchings (&) Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK e-mail: [email protected] Present Address: J. A. Lopez-Sanchez The Department of Chemistry, Stephenson Institute for Renewable Energy, University of Liverpool, Liverpool L69 7ZD, UK W. Zhou C. J. Kiely Department of Materials Science and Engineering, Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015-3195, USA K. Khalid SABIC Technology & Innovation, P.O. Box 42503, Riyadh 11551, Saudi Arabia
1 Introduction Zeolites are known to convert methanol to a wide range of hydrocarbons, including gasoline [1], olefins [2] and aromatics [3]. However, one of the major targets remaining is to maximise the selectivity to aromatic products using simple and highly reproducible catalyst preparation routes. Ga/ZSM-5 is a widely used catalyst to convert methanol to hydrocarbons, especially aromatic products, and it is typically prepared using gallium nitrate precursors dissolved and impregnated onto ZSM-5 [4]. However, despite the apparent simplicity, the impregnation of a zeolite with metal precursors is a complex process that can lead to the formation of metal or oxide nanoparticles, either inside or outside the zeolite pores [5, 6], and can generate framework or non framework gallium species [7]. However, during the synthesis most attention has focused on the reduction of Ga2O3 clusters [8] to generate Ga2O species, which in turn can migrate into the zeolite channels leading to cationic gallium species like: Ga3?, GaH? or GaH2? [9, 10]. This has led to catalysts capable of producing enhanced selectivity to aromatics in the methanol to hydrocarbons process [11–13]. In contrast, in the current work we wanted to specifically focus on the activity of extra framework species, like Ga2O3 on the external surface of the zeolite crystals, as to date this has received limited
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