Operando Raman to Enhance the Methanol-to-DME Conversion Over Non-Thermally-Pretreated Keggin Heteropolyacids

Abstract

Heteropolyacids (HPAs) are metal–oxygen clusters that are nowadays widely used in acid catalysis. Indeed, as they possess a very strong Bronsted acidity, approaching the superacid region, they generally allow performing reactions at lower temperatures than conventional catalysts. In the present paper, we use in situ/operando Raman spectroscopy to optimize the catalytic performance of H3PW12O40—the strongest Keggin-type HPA—in the low temperature (150 °C) gas phase dehydration of methanol to dimethyl ether (DME), which is one of the most promising renewable fuels for the future. Precisely, we demonstrate that the ability of methanol to displace the HPA’s crystallization water located in-between the Keggin units—and thus to reach the acidic protons—decreases with increasing temperature. Actually, we show that one and the same flow of methanol scarcely displaces the crystallization water at reaction temperature 150 °C, whereas, at a temperature as low as 25 °C, it succeeds to completely dehydrate the HPA. By...