Collaborative Research: Integrated Measurement and Predictive Modeling of Adsorbate Coverage and Compositional Effects on Catalytic Activity

Intellectual Merit. Understanding the coupling between reaction conditions and structure, mechanism, and kinetics at a heterogeneous catalytic surface remains a central challenge to rational catalyst development. It is well recognized today that the catalytic activity of a metal surface cannot be understood in isolation, but rather the catalyst and its reaction environment dynamically interact in often-complicated ways to create the observed, functioning catalyst system. Modern, high-pressure surface science techniques, such as high pressure x-ray photoelectron spectroscopy (HP-XPS) and scanning tunneling microscopy (HP-STM), can expose the structural and electronic transformations that occur under reaction conditions, but achieving the spatial and temporal fidelity necessary to understand catalysis at the atomic scale is challenging. Simulations based on density functional theory (DFT) are well suited to describing catalytic systems at the atomic scale, but direct exploration over the vast number of configurations of surface and adsorbate atoms is intractable. In past work two of the PIs have combined DFT simulations with cluster expansion (CE) techniques developed in the alloy theory community to tackle this configurational problem. The DFT-parameterized CEs provide a predictive model for the energy of any arrangement of atoms or adsorbates—information they have used in Monte Carlo simulations to predict surface structure and orderings, surface phase diagrams, coverage-dependent adsorption, and apparent reaction kinetics. Here we propose to integrate the DFT/CE methodology with precise atomic-resolution measurements under reaction conditions to validate and extend the capabilities of the approach to more realistic multicomponent, multidimensional, catalytically complex systems. In particular, we will extend the modeling approach to “ternary” systems involving ordering and reaction of multiple adsorbates at a surface, to “coupled-cluster” expansions to describe the effect of adsorption on the surface composition of a bimetallic catalyst, and to adsorbate-induced reconstructions. We choose as model systems ones that capture the relevant complexity but are amenable to both computational and experimental analysis. We focus in particular on catalysis involving the activation and reaction of O2 at metal surfaces—relevant to a range of problems in environmental catalysis. In particular, both temperature-programmed and operando studies using HP-XPS and HP-STM will be performed in house, on unique analytical platforms daily available, in parallel with DFT/CE simulations to characterize the surface/adsorbate system and kinetics of (a) catalytic CO and NO oxidation at Pt and Rh surfaces; (b) catalytic oxidation at the Pt/Rh bimetallic