Elucidating and exploiting the chemistry of Keggin heteropolyacids in the methanol-to-DME conversion: enabling the bulk reaction thanks to operando Raman

Operando Raman spectroscopy is used here to enlighten crucial and yet unconsidered aspects of the catalytic behavior of Keggin heteropolyacids (HPAs) in the gas phase dehydration of methanol to dimethylether (DME). On one hand, HPAs are since a long time claimed as being able to absorb methanol into their bulk, but on the other hand this feature is not yet really exploited when it comes to develop/use HPA-based catalysts for the methanol-to-DME process. Actually, the conditions in which the bulk is simultaneously accessible and catalytically active are not yet clearly reported. Clarifying this is precisely the aim of our work, for which we have used H3PW12O40 and H4SiW12O40. We precisely operando-follow the νs(W[double bond, length as m-dash]Ot) band reflecting whether methanol penetrates or not in the HPAs' bulk. We show that, when the HPAs are used without having been beforehand completely dehydrated, methanol penetrates into their bulk. However, the conversion remains low (