Integrated CO₂ capture and hydrogenation in presence of Ru–Na₂ZrO₃: an in-situ study

Integrated CO2 capture and conversion (ICCC) by hydrogenation is a promising strategy to utilize carbon dioxide and this work add to the effort to elucidate the catalytic hydrogenation mechanism using Ru based dual functional materials (DFM). Ru–Na₂ZrO₃ DFMs, obtained through different wet methods, were evaluated for the first time and the relationship between Ru and support systematically investigated. The thermally stable and cyclable Ru–Na₂ZrO₃-a (obtained without filtration step) exhibited CO₂ conversion of 80 % and a higher yield of CO at 400 °C compared to previously tested DFM, while the Na depleted/Zr rich Ru–Na₂ZrO₃-b resulted in 90 % selectivity to CH₄ with yield of 1.11 mmol/g at the same temperature. The in-situ experiments have provided conclusive evidence showing that CO2 hydrogenation on the two Ru DFMs is fundamentally different. In Ru–Na₂ZrO₃-a, the monoclinic Na₂ZrO₃ support acted as the active centre (not as promoter) for CO₂ bridging binding and hydrogenation to CH₄ at the metal-support interface through associative formate pathway with limited further reduction to methane due to lack of H2 spillover from the small and well dispersed Ru NPs, which results in CO desorption. Conversely, abundant clusters of larger Ru NPs in Ru–Na₂ZrO₃-b, led to CH₄ production due to co-existent Ru on-top direct dissociation of CO₂ (preferential) and monodentate formate adsorption and further methanation. Alkali zirconates doped metals, and their synthesis method could thus play a crucial role in designing tuneable heterogeneous catalysis in C₁ chemistry, which could significantly benefit the environment by lowering CO₂ levels, encouraging cleaner industrial practices, supporting a circular economy, and converting waste CO₂ into valuable products.