Size-Controlled Synthesis of Pd Nanocatalysts on Defect-Engineered CeO₂ for CO₂ Hydrogenation

The size effects of metal catalysts have been widely investigated to optimize their catalytic activity and selectivity. However, the size-controllable synthesis of uniform supported metal nanoparticles without surfactants and/or additives remains a great challenge. Herein, we developed a green, surfactant-free, and universal strategy to tailor the sizes of uniform Pd nanoparticles on metal oxides by an electroless chemical deposition method via defect engineering of supports. The nucleation and growth mechanism suggest a strong electrostatic interaction between the Pd precursor and low-defective CeO₂ and a weak reducing capacity for low-defective CeO₂, resulting in small Pd nanoparticles. Conversely, large Pd nanoparticles were formed on a highly defective CeO₂ surface. Combined with various ex situ and in situ characterizations, a higher intrinsic activity of Pd for the CO₂-to-CO hydrogenation was found on large Pd nanoparticles with higher electron density owing to their stronger H₂ dissociation ability and H-spillover effects, as well as the larger number of oxygen vacancies generated in situ for CO₂ activation under hydrogenation conditions.