Enhancing sintering resistance of atomically dispersed catalysts in reducing environments with organic monolayers

Abstract

Atomically dispersed precious metal catalysts maximize atom efficiency and exhibit unique reactivity. However, they are susceptible to sintering. Catalytic reactions occurring in reducing environments tend to result in atomically dispersed metals sintering at lower temperatures than in oxidative or inert atmospheres due to the formation of mobile metal-H or metal-CO complexes. Here, we develop a new approach to mitigate sintering of oxide supported atomically dispersed metals in a reducing atmosphere using organophosphonate self-assembled monolayers (SAMs). We demonstrate this for the case of atomically dispersed Rh on Al2O3 and TiO2 using a combination of CO probe molecule FTIR, temperature programmed desorption, and alkene hydrogenation rate measurements. Evidence suggests that SAM functionalization of the oxide provides physical diffusion barriers for the metal and weakens the interactions between the reducing gas and metal, thereby discouraging the adsorbate-promoted diffusion of metal atoms on oxide supports. Our results show that support functionalization by organic species can provide improved resistance to sintering of atomically dispersed metals with maintained catalytic reactivity.