X-Ray Imaging of SAPO-34 Molecular Sieves at the Nanoscale: Influence of Steaming on the Methanol-to-Hydrocarbons Reaction

Authors

  • Dr. Luis R. Aramburo,

    1. Inorganic Chemistry and Catalysis Group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (The Netherlands), Fax: (+31) 030-251-1027
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  • Dr. Javier Ruiz-Martínez,

    1. Inorganic Chemistry and Catalysis Group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (The Netherlands), Fax: (+31) 030-251-1027
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  • Dr. Linn Sommer,

    1. Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, N-0315 Oslo (Norway)
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  • Dr. Bjørnar Arstad,

    1. Department of Process Chemistry, SINTEF Materials & Chemistry, 0314 Oslo (Norway)
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  • Robison Buitrago-Sierra,

    1. Laboratorio de Materiales Avanzados, Departamento de Química Inorgánica, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain)
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  • Prof. Dr. Antonio Sepúlveda-Escribano,

    1. Laboratorio de Materiales Avanzados, Departamento de Química Inorgánica, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain)
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  • Prof. Dr. Henny W. Zandbergen,

    1. Kavli Institute of NanoScience, National Centre for High Resolution Electron Microscopy, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (The Netherlands)
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  • Prof. Dr. Unni Olsbye,

    1. Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, N-0315 Oslo (Norway)
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  • Prof. Dr. Frank M. F. de Groot,

    1. Inorganic Chemistry and Catalysis Group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (The Netherlands), Fax: (+31) 030-251-1027
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  • Prof. Dr. Bert M. Weckhuysen

    Corresponding author
    1. Inorganic Chemistry and Catalysis Group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (The Netherlands), Fax: (+31) 030-251-1027
    • Inorganic Chemistry and Catalysis Group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (The Netherlands), Fax: (+31) 030-251-1027
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Abstract

The effect of a severe steaming treatment on the physicochemical properties and catalytic performance of H-SAPO-34 molecular sieves during the methanol-to-hydrocarbons (MTH) reaction has been investigated with a combination of scanning transmission X-ray microscopy (STXM), catalytic testing, and bulk characterization techniques, including ammonia temperature programmed desorption and 27Al and 29Si magic angle spinning nuclear magnetic resonance. For this purpose, two samples, namely a calcined and a steamed H-SAPO-34 catalyst powder, have been compared. It has been found that calcined H-SAPO-34 displays a high selectivity towards light olefins, yet shows a poor stability as compared to a zeolite H-ZSM-5 catalyst. Moreover, in situ STXM at the carbon K-edge during the MTH reaction allows construction of nanoscale chemical maps of the hydrocarbon species formed within the H-SAPO-34 aggregates as a function of reaction time and steam post-treatment. It was found that there is an initial preferential formation of coke precursor species within the core of the H-SAPO-34 aggregates. For longer times on stream the formation of the coke precursor species is extended to the outer regions, progressively filling the entire H-SAPO-34 catalyst particle. In contrast, the hydrothermally treated H-SAPO-34 showed similar reaction selectivity, but decreased activity and catalyst stability with respect to its calcined counterpart. These variations in MTH performance are related to a faster and more homogeneous formation of coke precursor species filling up the entire steamed H-SAPO-34 catalyst particle. Finally, the chemical imaging capabilities of the STXM method at the Al and Si K-edge are illustrated by visualizing the silicon islands at the nanoscale before and after steaming H-SAPO-34.

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