Computational Study of C-C Coupling Reactions on Heterogeneous Catalysts

The utilization of carbon dioxide (CO2) in chemical production has attracted global research interest. Reacting CO2 with methane (CH4) removes these greenhouse gases from the atmosphere and turns both compounds into building blocks for organic compound synthesis. A commonly explored pathway involves dry reforming of methane (DRM), which reacts CH4 and CO2 to form syngas, a mixture of H2 and CO. Syngas is a widely used feedstock for synthesizing chemicals ranging from methanol to fuels via the Fischer-Tropsch (FT) process. However, DRM has a large positive ΔGº, which requires the reaction to be carried out at a high temperature (1000~1200 K) to achieve a favorable equilibrium constant. Therefore, DRM requires significant energy input, which contributes to instead of reducing greenhouse gas production. This research is focused on alternative routes for reacting CO2 with CH4 to avoid high energetic penalties. The fundamental premise is the formation of acetate (CH3COO) species on catalyst surfaces as a key intermediate toward producing organic compounds such as vinyl acetate, alkyl acetates, acetic anhydride, and cellulose acetate, all of which are important industrial chemicals. We perform computational modeling based on first-principles density functional theory (DFT) calculations to generate atomic-level insights that guide the design of heterogeneous catalysts for catalyzing methane carboxylation by CO2 (MCC) to form CH3COO. We investigate three types of catalytic materials, including ceria, pure metals, and alloys, to identify the factors that determine the effectiveness of these materials. Based on the insights, we propose single-atom alloys (SAAs) by doping a late d-metal (Ni and Cu) with a small amount of a more reactive metal (Zr, Hf, and Co). The catalytic advantage of the SAAs stems from stabilizing the CHx-CO2 coupling step at the more oxophilic dopant site while the host metal activates CH4. We also examine the functionalization of Cu by phenyl phosphonic acid (PPA) molecules to protect the metal surface from oxidation