Density Functional Theory-Driven Microkinetic Modeling and Experimental Validation Reveal the Promotional Effect of Cobalt in Ni Catalysts during Oxidative Dry Reforming of Methane

This study delves into the promotional effect of cobalt on supported nickel catalysts during oxygen-assisted dry reforming of methane. A comprehensive reaction mechanism for bimetallic Ni–Co catalysts has been lacking in the literature. We developed a microkinetic model using density functional theory to elucidate the impact of cobalt promotion on catalytic activity. Examining two bimetallic catalysts, Ni3Co and NiCo, we detected a negative nickel surface segregation energy. This indicates thermodynamic favorability for nickel segregation on the surface of Ni–Co catalysts. Climbing image nudged elastic band calculations were performed considering van der Waals interactions on surface reactions involving C–H and C–O bonds. These calculations revealed the following trend in activation energy: NiCo > Ni > Ni3Co. We established Brønsted–Evans–Polanyi (BEP) relationships for reactions involving C–H and C–O bonds, Ea = 1.09 ΔEdiss + 0.48 and Ea = 1.07 ΔEdiss + 0.60, respectively. Notably, our calculated activation energies and intercept of BEP relations were slightly lower than reported values due to zero-point energy corrections. We developed modified reaction mechanisms for NiCo and Ni3Co by incorporating our BEP relation into an existing nickel mechanism. Microkinetic simulations using the models yielded high predictive accuracy R2 > 0.95 for conversions. Our study identifies a critical cobalt threshold amount for optimizing nickel catalyst activity. The observed trend in cobalt promotion is attributed to the dual effect of dispersion and activation energy. This study deepens our understanding of the promotional role cobalt plays in Ni–Co catalysts, providing valuable insights for tailored catalyst design in methane reforming reactions.