Atomic Control of Surface Active Site Isolation in Pd₂Sn Nanocatalysts via Crystal Phase to Enhance Hydrogenation Selectivity

Crystal-phase modulation of nanocatalysts is an effective strategy for enhancing catalytic performance in heterogeneous catalysis by altering the surface electronic and geometric structures. However, accurately elucidating the relationship between chemical reactivity and surface atomic arrangement of nanocatalysts with distinct phases is a big challenge due to surface relaxation and reconstruction. Here, we achieved the phase transformation of Pd2Sn nanocatalysts from an orthorhombic to a hexagonal crystal structure by meticulously adjusting the thermal treatment conditions, thereby enhancing the selectivity of ethylene in the acetylene hydrogenation reaction to 93.7%, superior to most reported advanced catalysts. The atomic three-dimensional deciphering for the crystal phase effect of Pd2Sn nanocatalysts was revealed by a combination of atomic pair distribution function (PDF) and reverse Monte Carlo simulation (RMC). The results show that numerous Pd sites, characterized by a low Pd–Pd coordination number and highly isolated by Sn atoms, are present on the surface of Pd2Sn hexagonal phase nanocrystals. DFT calculations further verify that the unique local coordination structure of the Pd sites and the appropriate hybridization of the Pd 4d and Sn 5p orbitals on the surface of hexagonal phase Pd2Sn are crucial for attaining highly selective hydrogenation of acetylene.