Towards ALD thin film stabilized single-atom Pd1 catalysts

Abstract

Supported precious metal single-atom catalysts have shown interesting activity and selectivity in recent studies. However, agglomeration of these highly mobile mononuclear surface species can eliminate their unique catalytic properties. Here we study a strategy for synthesizing thin film stabilized single-atom Pd₁ catalysts using atomic layer deposition (ALD). The thermal stability of the Pd₁ catalysts is significantly enhanced by creating a nanocavity thin film structure. In situ infrared spectroscopy and Pd K-edge X-ray absorption spectroscopy (XAS) revealed that the Pd₁ was anchored on the surface through chlorine sites. The thin film stabilized Pd₁ catalysts were thermally stable under both oxidation and reduction conditions. The catalytic performance in the methanol decomposition reaction is found to depend on the thickness of protecting layers. While Pd₁ catalysts showed promising activity at low temperature in a methanol decomposition reaction, 14 cycle TiO₂ protected Pd₁ was less active at high temperature. Pd L₃ edge XAS indicated that the low reactivity compared with Pd nanoparticles is due to the strong adsorption of carbon monoxide even at 250 °C. These results clearly show that the ALD nanocavities provide a basis for future design of single-atom catalysts that are highly efficient and stable.