Single atom catalysts represent a new frontier in heterogeneous catalysis because of the promise of atom efficiency, higher reactivity and improved selectivity. A major challenge for this class of catalysts is achieving high metal loadings of dispersed single atoms. For industrial applications the single atoms also need to be thermally stable. One challenge that remains to be fully addressed is the poor thermal stability of isolated single atoms on oxide supports, especially when higher metal loadings are used, since the single atoms can agglomerate and transform into nanoparticles. Trapping single atoms is key to addressing this challenge. Herein, we report that DFT calculations have shown that Pt is bound strongly to cerium oxide forming a square planar complex, high surface area ceria exposes prominent (111) facets which do not exhibit the requisite four fold symmetry. By using a combination of Aberration corrected scanning transmission (AC-STEM), extended X-ray absorption fine structure (EXAFS) and density functional theory (DFT) calculations, we can determine the nature of trapping sites in an industrial catalyst support. We also show how the upper limit for loading single atoms on a support can be determined using a combination of XRD and TEM-EDS analysis. The surface concentration of 1 atom/nm<sup>2</sup> is confirmed by low energy ion scattering (LEIS) and from the metal loading and BET surface area. The high metal loadings of Pt (3wt%) present exclusively in single atom form, thermally stable at 800 °C in air. This work helps unravel how these single atoms are bound to the support, emphasizing the general principles behind atom trapping. The results also shed light on the redispersion of Pt-based catalysts. Oxidation is commonly used to reactivate catalysts poisoned by coke. Under these conditions transition metal oxides are created, hence trapping them on the support can help in achieving a fully regenerable catalyst.

Stabilizing high metal loadings of thermally stable platinum single atoms on an industrial catalyst support

2019 Fall National Meeting

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