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

Abstract

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.