(602a) Non-Faradaic Electrochemical Promotion of Brønsted Acid Catalysis

Temperature and reactant partial pressure are considered the typical handles for controlling reaction rates and product selectivities in gas-phase heterogeneous thermocatalytic systems. At fixed temperature and pressure, modification of rates and selectivities must largely be addressed through ex situ structural and compositional changes to the catalyst and support. Electrochemical systems, however, include the additional handle of the electrode potential, which can be finely controlled without modifying bulk process parameters. In the 1980s, Vayenas and coworkers demonstrated that the electrode potential could also be used for in situ modification of thermocatalytic systems via the electrochemical promotion of catalysis (EPOC). This phenomenon has typically been exploited via polarization of noble metal films deposited on solid ion conductors; however, it has never, to our knowledge, been used to enhance rates of reactions catalyzed by solid Brønsted acids. Isopropanol dehydration to propylene was used as a probe reaction to study the in situ modification of a molybdenum catalyst film deposited on a solid yttria-stabilized zirconia electrolyte. Upon polarizing the Mo film by +1.5 V, the rate of isopropanol dehydration was reversibly and non-Faradaically increased by 250%. The reaction rate was zero order in IPA partial pressure at open circuit; however, negative order behavior was observed at higher IPA partial pressures during polarization of +1.5 V. We hypothesize that anodic supply of oxygen ions from the solid electrolyte to the surface of the catalyst results in either the stabilization of surface intermediates that lead to propylene or reversible electrochemical Brønsted acid site generation. This proof of concept demonstrates the feasibility of combining the fine control of applied electrochemical potential in a typical thermocatalytic reaction system in order to reversibly and controllably modify the function of a catalytic material to affect redox-neutral catalysis over non-metallic sites.