Improving Ni Catalysts Using Electric Fields: A DFT and Experimental Study of the Methane Steam Reforming Reaction

Abstract

(Graph Presented) This work demonstrates the benefits of applying an external electric field to the methane steam reforming reaction (MSR) in order to tune the catalytic activity of Ni. Through combined DFT calculations and experimental work, we present evidence for the usefulness of an electric field in improving the efficiency of current MSR processes - namely by reducing coke formation and lowering the overall temperature requirements. We focus on the influence of an electric field on (i) the MSR mechanisms, (ii) the rate-limiting step of the most favorable MSR mechanism, (iii) the methanol synthesis reaction during the MSR reaction, and (iv) the formation of coke. Our computational results show that an electric field can change the most favorable MSR mechanism as well as alter the values of the rate constants and equilibrium constants at certain temperatures and, hence, significantly affect the kinetic properties of the overall MSR reaction. Both computational and experimental results also suggest that a positive electric field can impede the formation of coke over a Ni catalytic surface during the MSR reaction. Moreover, the presence of a negative electric field notably increases the rate constant and the equilibrium constant for the methanol synthesis reaction, which suggests a possible direct route from methane to methanol. Finally, a field-induced Brønsted-Evans-Polanyi (BEP) relationship was developed for C-H bond cleavage, C-O bond cleavage, and O-H bond formation over a Ni catalytic surface. Overall, this investigation strengthens our understanding of the effect of an electric field on the Ni-based MSR catalytic system and highlights the benefits of designing heterogeneous reactions under applied electric fields.