An electrochemical approach for designing thermochemical bimetallic nitrate hydrogenation catalysts

Classically, catalytic promotion in bimetallic catalysts has been ascribed to atomic-scale cooperativity between metal constituents. For catalytic reactions that could involve charge transfer, electron and ion flow may engender bimetallic promotion without atomic-level connectivity. Here we examine this hypothesis in the context of nitrate hydrogenation, a reaction catalysed almost exclusively by bimetallic catalysts. On state-of-the-art PdCu/C, nitrate hydrogenation to nitrite proceeds via electrochemical coupling of hydrogen oxidation and nitrate reduction half-reactions; Pd catalyses the former, while Cu catalyses the latter. Using this mechanistic framework, we predict how different Pd:Cu ratios affect nitrate hydrogenation rates, and rationalize the catalytic activity observed in PtAg/C and Ru/C. Finally, by only promoting the electrochemical hydrogen oxidation reaction with Ni(OH)₂, we synthesize PdNi(OH)₂Cu/C catalysts with comparable nitrate hydrogenation activity to our best-performing PdCu/C using fivefold less Pd. This work provides an alternative strategy for designing alloy catalysts for thermochemical redox transformations.