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

Abstract

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.