Dehydration of ethanol catalyzed by H3-xCsxPW12O40 has been studied by a transient response method and solid-state NMR spectroscopy. An unusual pressure dependency was observed for catalysts with x ≤ 2. This has been explained by assuming (1) that C2H5OH+2 and (C2H5OH)2H+ act as intermediates for the formation of ethylene and ether, respectively, in the pseudoliquid phase and (2) that the concentrations of these intermediates are determined by protonation equilibria established in the system. The presence of these species as well as of an ethoxy group has been detected directly by solid-state NMR spectroscopy in the case of H3PW12O40. Dehydration over H0.5Cs2.5PW12O40 proceeded by surface reaction as in the case of ordinary acid solids.
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