| AVS 65th International Symposium & Exhibition | |
| Surface Science Division | Wednesday Sessions |
| Session SS+HC-WeM |
| Session: | Catalytic Alloys: Understanding Heterogeneity |
| Presenter: | Judith Yang, University of Pittsburgh |
| Authors: | S. House, University of Pittsburgh C.S. Bonifacio, University of Pittsburgh J. Timoshenko, Stony Brook University P. Kunal, University of Texas at Austin H. Wan, University of Texas at Austin Z. Duan, University of Texas at Austin H. Li, University of Texas at Austin J.C. Yang, University of Pittsburgh A.I. Frenkel, Stony Brook University S. Humphrey, University of Texas at Austin R. Crooks, University of Texas at Austin G. Henkelman, University of Texas at Austin |
| Correspondent: | Click to Email |
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. Additionally, variation in the elements’ mixing patterns and reconfiguration can affect the reaction mechanisms and thus catalytic performance [1]. 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 correlative theory-experiment design approach for addressing this issue, through application to the complex structures of Rh/Au bimetallic hydrogenation catalysts. Our calculations predict this system to exhibit superior allyl alcohol hydrogenation performance compared to single-element catalysts due to the ability to tune the hydrogen binding on the surface [2]. In this study, Rh/Au bimetallic NPs of different metal mixing ratios were synthesized via microwave heating and characterized using synchrotron extended X-ray absorption fine structure (EXAFS) spectroscopy and scanning transmission electron microscopy (STEM). EXAFS samples particle ensembles to extract information about atomic bonding (coordination, bond distances, etc.). TEM provides direct local characterization, down to the atomic scale, of particle size, morphology, and elemental distribution. The conventional approach to interpreting EXAFS – fitting to bulk reference spectra – is problematic for bimetallic NPs. We overcome this by using the STEM data to inform the generation of metal NP structures, calculated using interatomic potentials under the frame work the modified embedded-atom method (MEAM). EXAFS spectra for these structures were simulated and compared against the experimental EXAFS to iteratively refine the models, producing more atomic structures that were consistent with all experimental data, and will be more accurate for subsequent theoretical calculations. This work demonstrates that correlating the local characterization of TEM with the many-particle information from EXAFS grants a multiscale understanding not achievable with either approach alone.
[1] R. Ferrando, J. Jellinek, R.L. Johnston, Chem. Rev. 108 (2008), p. 845-910.
[2] S. Garcia, et al., ACS Nano 8 (2014), p. 11512-11521.