Using Support\nEffects to Increase the Productivity\nof Immobilized Ruthenium Hydride Catalysts for the Hydrogenation of\nCO<sub>2</sub>

Interfaces between catalytically active metal surfaces/sites\nand\nmetal oxides (such as those formed by metal oxides covering metal\nnanoparticles by strong metal–support interactions) allow both\nthe metal and metal oxide to react with substrates simultaneously\nand are important for the activity of many heterogeneously catalyzed\nreactions. However, similar interactions for well-defined immobilized\ncatalysts have not been investigated, despite their potential for\nincreasing catalytic activity. We test the reactivity of a ruthenium\nhydride [H<sub>2</sub>Ru(PPh<sub>3</sub>)<sub>2</sub>(Ph<sub>2</sub>P)<sub>2</sub>NC<sub>3</sub>H<sub>6</sub>Si(OEt)<sub>3</sub> (<b>1</b>)] in the amine-promoted hydrogenation of CO<sub>2</sub> as\nboth a homogeneous catalyst and anchored on SiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, ZnO, and SBA-15. Anchoring <b>1</b> on\nthe surfaces resulted in varying degrees of surface collapse (formation\nof H–Ru–O linkages to the surface), with ZnO and confinement\nin SBA-15 pores giving the least surface collapse. Immobilization\nof <b>1</b> on ZnO gave a 6-fold improvement of the catalytic\nrate over the corresponding homogeneous catalyst. This increase in\nthe catalytic productivity was only possible when the complex was\nin close contact with ZnO and is most likely due to a combination\nof increased catalytic activity and slower deactivation. These results\ndemonstrate the ability of surface effects to vastly improve the productivity\nof even mediocre catalysts upon surface immobilization.