A Combined Experimental and Theoretical Study on the Hydrolysis of Dimethyl Ether over H-ZSM-5

Abstract

The catalytic hydrolysis of dimethyl ether (DME) over H-ZSM-5 was examined by experimental and theoretical studies. We experimentally observed that this reaction yields methanol as major product at low temperature (<300 °C) but produces other carbon-containing species at temperature above 300 °C. The insight into the reaction mechanisms of DME hydrolysis have been investigated by the M06/6-31G(d,p) method using the 128T cluster model of H-ZSM-5. Our calculations showed that DME hydrolysis catalyzed by H-ZSM-5 occurs via two mechanisms, stepwise and concerted. For the stepwise mechanism the reaction starts with (i) the demethylation of DME to form a surface methoxide intermediate, followed by (ii) the hydrolysis between the methoxide intermediate and a water molecule to produce methanol as the product. The calculated activation barriers for the demethylation and hydrolysis steps are 168.6 and 81.8 kJ·mol–1, respectively. For the concerted manner, the demethylation and hydrolysis take place simultaneously i...