Hydrogenation of CO2 over Ru/YSZ Electropromoted Catalysts

The effect of electrochemical promotion of catalysis (EPOC or NEMCA effect) was investigated for the hydrogenation of CO2 using Ru catalyst electrodes supported on YSZ solid electrolyte pellets at temperatures 200-300 degrees C and ambient pressure. Methane was found to be the main reaction product at temperatures up to 240 degrees C, whereas CO dominated at higher temperatures. It was found that the O2- supply to the Ru surface causes a significant increase in the CH4 formation rate and selectivity, accompanied by a significant decrease in the rate of CO formation. This is a very rare case in which electrochemical promotion is found to promote a catalytic reaction and at the same time to poison a reaction proceeding in parallel with the promoted one. The faradic efficiency values were found to be on the order of 10-10(3), which are among the highest reported in the EPOC hydrogenation literature. The kinetic and electropromotion results can be interpreted, using the rules of electrochemical promotion, in terms of the changes in the surface RuOx/Ru ratio induced via potential application, as observed via ex situ XPS.