Comparative Study of the Electrochemical Promotion of CO sub(2) Hydrogenation over Ru-Supported Catalysts using Electronegative and Electropositive Promoters

The kinetics and the electrochemical promotion of the hydrogenation of CO sub(2) over Ru-catalyst electrodes deposited on yttria-stabilized zirconia (YSZ) and (Na super(+))- beta "-Al sub(2)O sub(3) solid electrolytes are investigated at temperatures between 200 and 340 degree C and pressures up to 5bar. In the case of both the O super(2-) conductor (YSZ) and the Na super(+) conductor ( beta "-Al sub(2)O sub(3) ), the selectivity for CH sub(4) production is enhanced significantly when using a positive potential by supplying of O super(2-) to, or removal of Na super(+) from, the catalyst surface. The opposite effect is observed when using a negative applied potential, which suppresses CH sub(4) formation and enhances the production of CO through the reverse water-gas shift reaction. However, at low Na coverage, and under reducing conditions, both methanation and H sub(2) production are promoted by the application of a negative potential. The observed electrochemical promotion behavior in conjunction with the reaction kinetics is consistent with the rules of electrochemical and chemical promotion. Who's the boss? A comparison of the electrochemical promotion of CO sub(2) hydrogenation over Ru-catalyst electrodes deposited on beta "-Al sub(2)O sub(3) (see picture) or YSZ solid-electrolyte pellets, at temperatures between 200 and 340 degree C and pressures up to 5bar, shows that CH sub(4) production is enhanced by applying a positive potential (electronegative promoter supply), whereas negative-potential (electropositive-promoter supply) favors CO formation.