The acceleration of rational catalyst design by computational simulations is only practical if the theoretical structures identified can be synthesized and experimentally verified. Bimetallic catalysts have the potential to exceed the selectivity and efficiency of a single-component system, but adding a second metal greatly increases the complexity of the system. Most experimental tools for the characterization of nanoparticles (NPs) provide structural data at the relevant length scales, but not enough to unambiguously determine the structure. Here we present our application of a correlative theory-experiment design approach to characterize Rh/Au and Rh/Ag bimetallic hydrogenation catalysts, which our calculations predict to have superior allyl alcohol hydrogenation performance compared to single-element catalysts due to the ability to tune the hydrogen binding on the surface [1]. In this study, Rh/Au and Rh/Ag bimetallic NPs of different metal mixing ratios were synthesized via microwave heating and characterized under a range of environmental conditions. Synchrotron extended X-ray absorption fine structure (EXAFS) spectroscopy was used to determine the average coordination number, interatomic distance, and disorder in the materials  through fitting to reference structures. Small metal NP structures were calculated by density functional theory (DFT) and interatomic potentials under the frame work the modified embedded-atom method (MEAM) were employed to simulate EXAFS spectra. To accurately inform the input models, scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) were employed to measure the particle size, morphology, and elemental distributions. Correlating the local characterization of TEM with the many-particle information from EXAFS, grants a multiscale understanding not achievable with either approach alone.

Computationally assisted STEM and EXAFS characterization of tunable Rh/Au and Rh/Ag bimetallic nanoparticle catalysts

254th National Meeting (2017)

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