Quantifying the Site Heterogeneities of Non-Uniform Catalysts Using QuantEXAFS

Abstract

We present the Multi-site (MS) QuantEXAFS approach, designed to model the EXAFS data from samples containing an element in different local bonding geometries. Building upon our QuantEXAFS method, which maps experimental extended X-ray absorption fine structures (EXAFS) data to DFT-optimized structures, MS-QuantEXAFS introduces the key capability to probe fractional contributions of multiple sites that may be present in an experimental sample. Specifically, we demonstrate effectiveness of this technique by investigating mixed samples containing known fractions of site-isolated subsurface Pt/MgO with Pt nanoparticles uniformly supported on MgO. The ‘site-fractions’ obtained through MS-QuantEXAFS closely match (i. e., ±6%) the known fractions of the physically mixed samples. This approach has been generalized to other oxides, and thus represents an important advance in quantifying the speciation of non-uniform catalyst samples.