Non-Faradaic Electrochemical Promotion of Bronsted Acid-Catalyzed Dehydration Reactions over Molybdenum Oxide

We report the non-Faradaic electrochemical promotion of a Bronsted acid-catalyzed reaction over a metal oxide surface. Isopropanol dehydration to propylene was used as a probe reaction to study the in situ modification of a molybdenum catalyst film deposited on a yttria-stabilized zirconia solid electrolyte. Upon polarizing the Mo film by +1.5 V, the rate of isopropanol dehydration (1.2 kPa IPA, 3.3 kPa O-2, 673 K, 135 kPa total pressure) was enhanced by 2.5x. Smaller rate enhancements of c.a. 1.3x were also observed for 2-butanol dehydration to butenes over the same catalyst. Although electrochemical dehydration pathways for this chemistry are implausible, by postulating a hypothetical Faradaic dehydration route, we calculate Faradaic efficiencies greater than 100 for IPA dehydration, confirming the non-Faradaic nature of the promotional effect. This effect is reversible and does not appear to permanently alter the chemistry of the Mo film, based on XPS analysis. We hypothesize that this promotion originates from generation of Bronsted acid sites localized to the three-phase boundary at the catalyst/gas/electrolyte interface and/or acid site strengthening due to electrical polarization. This work demonstrates an alternative handle to promote catalytic turnover, which with further understanding, could be applied toward other Bronsted acid-catalyzed chemistries.