TiO2-supported heteropoly acids for low-temperature synthesis of dimethyl ether from methanol

The production of dimethyl ether via methanol dehydration with TiO2-supported H3PW12O40 (HPW) or H4SiW12O40 (HSiW) catalysts has been studied. Both supported heteropoly acids (HPAs) exhibit superior performances in terms of methanol conversion rate and selectivity toward dimethyl ether at significantly lower temperatures than benchmark Al2O3- and ZSM-5-based catalysts. Both supported and unsupported heteropoly acids have strong Brønsted acid sites; however, the TiO2-supported HPAs have a lower amount of acid sites than the bulk HPA. In addition, upon HPA deposition on TiO2, the water of crystallization molecules, located between neighboring Keggin structures, becomes adsorbed more weakly, so they can be easily replaced by methanol molecules. As a result of the higher accessibility of methanol to the active acid sites of the supported heteropoly acids, both H3PW12O40/TiO2 and H4SiW12O40/TiO2 exhibit higher normalized rates for methanol conversion and total DME production than unsupported HPAs.