The CsxH3―xPW12O40 catalysts microstructure model

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 CsxH3 - 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 CsxH3 - xPW12O40 containing spherical aggregates, which consist of Cs3PW12O40 crystallites core coated with H3PW12O40 layers, was proposed on the basis of the structuralatextural 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 Cs2.5H0.5PW12O40 due to its special microstructure: a H3PW monolayer embedding a core of Cs3PW. The Cs concentrations on the CsxH3 - 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.