(389av) Unveiling the Role of Interfacial Species in Methane Dry Reforming on CeO2 Supported Nin Catalysts - a Combined Density Functional Theory and Microkinetic Modeling Study

Mitigating greenhouse gas emissions is imperative, and dry reforming of methane (DRM) is a promising avenue for upcycling two of the most potent GHGs. CH₄ and CO₂ are converted into syngas (H₂ and CO), which can be used as the feed for Fischer-Tropsch processes. Small Ni metal particles supported on oxides have demonstrated strong potential as DRM catalysts. Ni is known for its excellent activity towards CH₄ activation. However, catalyst deactivation due to carbon deposition at high operating temperatures remains a major bottleneck. The use of a redox active oxide support such as CeO₂ can perform dual roles – providing oxygen to Ni for C oxidation and activating CO₂ at the resulting oxygen vacancies. A detailed mechanistic understanding of the O-transport and the involvement of activated CO₂ in CH₄ activation on Ni_n supported CeO2 catalysts remains limited.

We probe the role of oxide-metal interface in promoting interfacial reaction rates and stabilizing reaction intermediates using Density Functional Theory (DFT) calculations (catalyst model - Ni_n/CeO₂) along with microkinetic modeling (MKM). DFT calculations reveal a 1.5 eV barrier for O-migration across the oxide support. Interestingly, CO₃^2- like species significantly lower this barrier, enabling near-barrierless O-migration. Degree of rate control analysis on our multi-site MKM identifies O-transport across the interface (from support to the metal) as one of the rate-determining steps. We hypothesize that the enhanced stability of CO₃²⁻ species proximal to metal-oxide interfaces could similarly result in facile interfacial O-transport, thereby mitigating coke formation and potentially altering the rate-determining steps. Oxygenate interfacial species also participate in CH₄ activation, decreasing the reaction energy required for the first C–H bond cleavage by at least 0.5 eV, unveiling alternative CH₄ activation pathways. The mechanistic relevance and kinetic dominance of these pathways is further confirmed by a DFT-based MKM analysis. These observations are also tested for larger metal particles (low dispersion) to capture any shifts in kinetic regime. Altogether, this work offers mechanistic insights into interfacial events occurring in DRM as a function of metal dispersion, advancing the understanding of oxide–metal interfaces in catalytic systems.