Hyper-Cross-Linked\nPolymer-Based Self-Supported Reusable\nRu-NHC Catalyst for Amine-Assisted Hydrogenation of CO<sub>2</sub> to Methanol

Research on the capture and catalytic conversion of CO<sub>2</sub> to valuable chemicals and alternative fuel candidates has\nmultifaceted\nrelevance from the perspective of sustainable development goals (SDGs).\nMethanol, advocated as an alternative fuel, can be produced via amine-assisted\nintegrated capture of CO<sub>2</sub> and the subsequent hydrogenation\nvia a formamide intermediate. Notably, amines not only function as\nCO<sub>2</sub>-capturing agents but also assist in crucial H<sub>2</sub> activation by a metal catalyst during a series of hydrogenation\nsteps to form methanol. Toward implementation of this cascade strategy\nof amine-assisted hydrogenation of CO<sub>2</sub> to MeOH, herein,\nwe developed an NHC-based pincer ligand-bound homogeneous molecular\nRu catalyst (<b>Ru-1</b>), which was then translated into a\nporous hyper-cross-linked polymer (HCP)-based self-supported single-site\nheterogeneous catalyst, termed as <b>HCP-Ru-1</b>. Initially,\na control mechanistic investigation was performed in order to get\ninsights into the crucial H<sub>2</sub> activation step at the Ru\ncenter of the catalyst assisted by the amine used in the reaction.\nNext, the formation of the formamide intermediate by both catalyst\ncandidates <b>Ru-1</b> and <b>HCP-Ru-1</b> was probed\nand confirmed, employing several amines in the presence of pressurized\nCO<sub>2</sub> and H<sub>2</sub> at a relatively mild temperature\nof 120 °C, where the catalysts exhibited turnover numbers (TONs)\nup to 3520 and 15,750, respectively, indicating their high catalytic\nefficiency. Finally, for the catalytic CO<sub>2</sub>-to-MeOH production\nreaction, a polyamine, namely, pentaethylenehexamine (PEHA), was used\ndue to its high efficiency in CO<sub>2</sub> capture as well as ability\nto act as a suitable organic base for deprotonative H<sub>2</sub> activation,\nand the <b>Ru-1</b> and <b>HCP-Ru-1</b> systems displayed\nsingle-run TONs of 400 and 1150, respectively. As the most significant\nadvancement in this process, the heterogeneous <b>HCP-Ru-1</b> catalyst turned out to be highly reusable, and in a 10-cycle reuse\ndemonstration experiment, it achieved a cumulative TON of 10,370 with\nmerely 1.13% loss in activity per cycle.