Crystal-Phase Engineering of PdCu Nanoparticles for Catalytic Reduction of NO by CO

Tuning the crystal phase of bimetallic nanoparticles has emerged as a promising strategy to boost their catalytic performance, but identifying the active site at the single-nanoparticle scale is rarely done and remains challenging. Here, the crystal phase of a PdCu single nanoparticle, spatially confined by a silica shell, was mediated between the ordered body-centered cubic (B2) phase and the disordered face-centered cubic (A1) phase. During the crystal-phase transition, the porous silica shell prevented the bimetallic nanoparticles from sintering under reactive gases and at elevated temperatures, enabling us to alter the crystal phase while keeping the particle size and atomic composition unchanged. Combined microscopic and spectroscopic characterizations revealed that the B2 particle was enclosed predominantly by the {110} facets over which Pd and Cu atoms were populated alternatively, while the A1 particle exposed mainly the {111} facets terminated by a random distribution of Pd and Cu atoms. When applied to catalyze NO reduction by CO, the B2 particle showed a much higher activity with a reaction rate of 4.5 times greater than that of the A1 particle. It was proposed that the orderly arranged Pd and Cu atoms on the {110} facets, exposed by the B2 particle, favored the coadsorption of NO and CO and further facilitated the dissociation of NO as the rate-determining step in the reaction network.