Selective Catalytic Production of Urea: Unravelling the Pairwise Competition on p-d Alloy Catalysts

Constructing asymmetric structures facilitates electrocatalytic urea synthesis by enabling targeted reactant activation. However, accurate mechanistic understanding is complicated by intricate pairwise competitions among initial adsorption, C-N coupling, and parasitic hydrogenation. Herein, by decoding these competitive routes on indium-based coinage metals (In₄M₉, M = Au, Ag, and Cu), we systematically uncover an intrinsic activity sequence of Ag > Cu > Au. To rationally evaluate these disparate pathways, we deduce two quantifiable stage-specific descriptors: the Anchoring Affinity (S_anchor) for assessing robust reactant capture against proton attack, and the Coupling Propensity (S_couple) for evaluating C-N combination likelihood over fatal hydrogenation. A desired catalytic zone is defined from seven alloy systems under the quantitative criteria of S_anchor < 0 and -0.3 < S_couple < -0.12. Strikingly, In₄Ag₉ falls precisely into this desired zone, driving urea synthesis with a minimal limiting energy of only 0.31 eV. Electronic analyses reveal that In₄Ag₉ affords an appropriate NO activation, maintaining an ideal thermodynamic balance between NO reduction and C-N coupling. Ultimately, this work unravels the atomic-level pairwise mechanisms and provides straightforward, quantifiable descriptors as a powerful compass to guide targeted catalyst design.