Density Functional\nTheory-Driven Microkinetic Modeling\nand Experimental Validation Reveal the Promotional Effect of Cobalt\nin Ni Catalysts during Oxidative Dry Reforming of Methane

This study delves into the promotional effect of cobalt\non supported\nnickel catalysts during oxygen-assisted dry reforming of methane.\nA comprehensive reaction mechanism for bimetallic Ni–Co catalysts\nhas been lacking in the literature. We developed a microkinetic model\nusing density functional theory to elucidate the impact of cobalt\npromotion on catalytic activity. Examining two bimetallic catalysts,\nNi<sub>3</sub>Co and NiCo, we detected a negative nickel surface segregation\nenergy. This indicates thermodynamic favorability for nickel segregation\non the surface of Ni–Co catalysts. Climbing image nudged elastic\nband calculations were performed considering van der Waals interactions\non surface reactions involving C–H and C–O bonds. These\ncalculations revealed the following trend in activation energy: NiCo\n> Ni > Ni<sub>3</sub>Co. We established Brønsted–Evans–Polanyi\n(BEP) relationships for reactions involving C–H and C–O\nbonds, <i>E</i><sub>a</sub> = 1.09 Δ<i>E</i><sub>diss</sub> + 0.48 and <i>E</i><sub>a</sub> = 1.07\nΔ<i>E</i><sub>diss</sub> + 0.60, respectively. Notably,\nour calculated activation energies and intercept of BEP relations\nwere slightly lower than reported values due to zero-point energy\ncorrections. We developed modified reaction mechanisms for NiCo and\nNi<sub>3</sub>Co by incorporating our BEP relation into an existing\nnickel mechanism. Microkinetic simulations using the models yielded\nhigh predictive accuracy <i>R</i><sup>2</sup> > 0.95\nfor\nconversions. Our study identifies a critical cobalt threshold amount\nfor optimizing nickel catalyst activity. The observed trend in cobalt\npromotion is attributed to the dual effect of dispersion and activation\nenergy. This study deepens our understanding of the promotional role\ncobalt plays in Ni–Co catalysts, providing valuable insights\nfor tailored catalyst design in methane reforming reactions.