Synthesis of perovskite polyhedron nanocrystals with equivalent facets and the controlled growth of Pt nanoparticles with differing surface concentration of oxidized Pt4+/Pt2+ species

Abstract

Co-existence of different surfaces in traditional polycrystalline heterogeneous catalysts imposes a challenge to induce different kinds of catalytic species and average reactivity. Supported metal/oxide model catalyst designed with equivalent well-defined surfaces and active species provides an opportunity to control the uniformity, maintain efficient activity, and understand catalytic mechanisms at the atomic and molecular levels. Herein, sub-20 nm perovskite-structure BaTiO3 polyhedron nanocuboids and Zr-substituted rhombic dodecahedron nanocrystals were synthesized and employed as the oxide support for the subsequent uniform growth of 1–2 nm Pt nanoparticles. These Pt nanoparticles were well dispersed on the 12 equivalent (110) facets of BaTi0.75Zr0.25O3 rhombic dodecahedra and on the 6 equivalent (100) facets of BaTiO3 nanocuboids. The main active centers on the Pt/BaTi0.75Zr0.25O3 catalysts in the oxidized surface layer of Pt (111) facets are Pt4+ versus Pt2+, which is in contrast to the oxidized surface layer of the Pt (100) facets on the Pt/BaTiO3 cuboids where there are a greater number of Pt2+ species. Compared with Pt/BaTiO3 nanocuboids, the Pt/BaTi0.75Zr0.25O3 catalysts demonstrated higher CO catalytic oxidation activity with a lower apparent Arrhenius activation energy. This work advances our ability to synthesize metal/oxide model catalyst that offer equivalent facets and highly uniform active centers with reasonable surface area in order to gain insight in reaction mechanisms.