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.