Theoretical and Experimental Insights into CO2 Capture and Methanation over Amine-Grafted Ru-Based Catalysts

Carbon capture and storage (CCS) technologies, along with CO2 capture and conversion methods, have emerged as crucial research areas to address rising CO2 emissions. In this study, we seek to understand the mechanistic role of amines in enabling lower-energy pathways for CO2 conversion. Our research focuses on the development and analysis of dual-functional materials (DFMs) engineered for the reactive capture and conversion (RCC) of CO2 into methane, utilizing Ru catalysts grafted with amine groups. We employ Density Functional Theory (DFT) calculations using methylamine as a model amine to investigate the impact of amine groups on CO2 methanation on a Ru(0001) surface, both in the presence and absence of amine groups. The amine ligand alters the carbon coordination environment, promoting direct C-O dissociation and potentially destabilizing the CO* adsorbate, thereby reducing the risk of CO poisoning. Additionally, we observe a preference for hydrogenation, although it becomes more energetically uphill in the amine-bound scenario. Our experiments, however, report similar CO2 conversion and CH4 production rates over the synthesized catalysts "Ru/TiO2" and the amine (N-(2-aminoethyl)-3-aminoproplytrimethoxysilane ("diaminosilane")) deposited catalyst "Diamine-Ru/TiO2". By constructing comparative reaction-free energy diagrams and performing microkinetic modeling (MKM) simulations, we link our theoretical findings with experimentally observed CO2 uptake, conversion, and methane production rates. A microkinetic model was employed to investigate the anomaly, showing reduced amine-carbon complex coverage and increased CO2 coverage at all temperatures. The MKM simulations consistently confirmed these trends. This comprehensive approach offers key insights into the role of the amine-CO2 bond in methanation, highlighting a pathway toward lower-energy, more efficient CO2 capture and conversion processes.