Both sites must turn over in tandem catalysis: Lessons from one-pot CO₂ capture and hydrogenation

By combining capture and catalytic conversion of carbon dioxide to chemicals and fuels in a single process operation, one can potentially increase the efficiency and feasibility of waste carbon utilization. We report here results for CO₂ capture using amines supported on high-surface-area silicas, including fumed silica and mesoporous SBA-15, in tandem with a homogeneous ruthenium hydrogenation catalyst in a batch reactor system, and compare these with previous reports for two- and three-phase versions of capture + hydrogenation systems. While diamine- and polyamine-functionalized solid capture agents led to higher methanol productivities than homogeneous amine and homogeneous catalyst combinations, turnover of the amine capture sites is a significant limitation that has not been previously recognized. These results demonstrate that tandem catalysis in these systems has not yet been achieved, despite previous claims to the contrary.