(233f) Understanding Catalyst Nuclearity and Local Coordination at Interfaces to Control CO2 Hydrogenation

There are two themes of our work, one involving controlling the binding of reactive molecular species at the active site and the other involving creating adjoining reactive sites having dissimilar electronic properties but acting in concert to catalyze reactions at interface. Two strategies have been developed, first (i) varying the proportion of the two active phases in the catalyst and then by (ii) adjusting the nuclearity or composition of one of the phases to vary its reactivity. The effects of tuning both the proportion and nuclearity of the active phases have been demonstrated for the reduction of CO₂ to CO and methanol, which are classes of reactions that are known to require interfaces in order to achieve high selectivity.

In the first we stabilized sub-nanometer Cu and Pd species at defect sites inside metal organic frameworks (MOFs) having either ZrO₂ or ZnO₂ nodes. This allowed us to modify the proportion of interfaces with higher control than in typical approach of varying the size of metal particles supported by bulk oxides. For the second system, we either stabilized single atoms of noble metals (e.g., Rh, Pt, and Ru) at the surface of bulk magnetite (Fe₃O₄) or, as an inverse approach, we deposited small FeO₂ domains onto the Rh metal particles. Both strategies allowed us to maximize the binding coverage of active carbonaceous species while still retaining the ability of the catalysts to activate H₂. During this work, we quantitatively show how the coverages of adsorbed species and the barriers for H addition and C-O bond cleavage are controlled by nuclearity of active phases and environment at interfaces. As a consequence, we report rational strategies for tuning the activity and selectivity of a variety of catalysts for CO₂ hydrogenation to CO or methanol.