The CsxH3 − xPW12O40 catalysts microstructure model

Authors: V.Z. Sasca, O. Verdes, L. Avram, A. Popa, A. Erdőhelyi, A. Oszko

Abstract:
The salts of the H₃PW₁₂O₄₀ (H₃PW) with Cs counter cation were prepared and characterized by thermal analysis, IR, XRD, BET, XPS LEIS and SEM methods. The samples are denoted as Cs_xH₃ − _xPW₁₂O₄₀ (x = 1, 2, 2.25, 2.5 and 3). The catalytic activity of the compounds prepared with various cesium/Keggin unit ratios was tested in ethanol conversion by pulse reaction technique. The change of catalytic activity vs. pulse number was explained by formation of strong adsorbed species on catalysts. A microstructure model of the Cs_xH₃ − xPW₁₂O₄₀ containing spherical aggregates, which consist of Cs₃PW₁₂O₄₀ crystallites core coated with H₃PW₁₂O₄₀ layers, was proposed on the basis of the structural–textural properties and their catalytic performances in ethanol conversion. The model explains the abrupt increase of the specific surface area for x > 2 and also the highest selectivity for C₄ hydrocarbons on Cs_2.5H_0.5PW₁₂O₄₀ due to its special microstructure: a H₃PW monolayer embedding a core of Cs₃PW. The Cs concentrations on the Cs_xH₃ − _xPW₁₂O₄₀ surface were determined by XPS and were found less than expected based on their chemical composition, but which correspond to the proposed model of microstructure.

Keywords:
Heteropoly compounds
Cesium tungstophosphates
Keggin structure
Ethanol conversion
Microstructure model

Published in: Applied catalysis A: General  (Volume 451, Pages 1-288, 31 January 2013)

Publisher: Elsevier

ISSN Information: 0926-860X

The CsxH3 − xPW12O40 catalysts microstructure model

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