Applications of the Electrochemical Promotion of Catalysis in Methanol Conversion Processes

Abstract

In this work, three possible applications of the phenomenon of electrochemical promotion of catalysis (EPOC) are demonstrated for methanol conversion processes: enhancement of the catalytic activity, modification of the catalytic selectivity and partial oxidation of the catalyst. For that purpose, a Ni catalyst film prepared via a physical vapour deposition technique was electrochemically promoted by K⁺ in different methanol conversion reactions for hydrogen production. Under methanol decomposition and steam reforming conditions, application of certain negative overpotentials and subsequent back-spillover of K⁺ promoter ions led to an increase in the Ni catalytic activity through electrophilic EPOC behaviour. On the other hand, under methanol partial oxidation conditions, the K⁺ ions caused a decrease in the catalytic selectivity toward H₂ and CO while they favoured selectivity toward CO₂ and H₂CO. This effect was explained by an increase in the Ni oxidation state due to O₂ activation induced by K⁺ ions, as shown by post-reaction X-ray diffraction analysis. All the potassium-induced effects were reversible between negative and positive polarizations. This shows the different possibilities of the EPOC phenomena on nickel catalysts in heterogeneous catalysis. Specifically, the in situ modification of catalytic activity and selectivity in methanol conversion reactions would be interesting for on-board hydrogen production processes, where the attenuation of catalyst deactivation and the control of metal oxidation state would also play a key role.