(765f) Platinum Restructuring By Carbon Monoxide and Stabilization As Single Atoms in Metal Matrices

Authors: 
Cao, S., Tufts University
Liu, Y., Tufts University
Annamalai, L., Tufts University
Deshlahra, P., Tufts University
Flytzani-Stephanopoulos, M., Tufts University
Heterogeneous catalysts play a vital role in the chemical industry for the production of most commodity and specialty chemicals, upgraded fuels, and for energy generation and food production. However, the co-existence of single atoms, clusters, and nanoparticles (NPs) of supported metal catalysts hinders the identification of active sites and thus the development of more efficient chemical processes. For reactions that are catalyzed by supported single metal atoms of proper coordination, there are new opportunities afforded. Their properties are distinct from those of supported metal nanoparticles. Non-metallic [Au-Ox]- and [Pt-Ox]- species anchored on oxide supports were demonstrated as the active sites for low-temperature WGS (1), which were later shown as single atom-centered species (2,3). Besides oxide supports, metal matrices can be used as the host to stabilize single isolated metal atoms forming single atom alloy catalysts, such as Pd1Cu and Pt1Cu (4,5). Single atom alloys were recently demonstrated to catalyze the dehydrogenation of butane to butenes(6), propane dehydrogenation to propylene (PDH) (7). Here, we report a simple method that uses CO to disaggregate Pt nanoparticles (NPs) on TiO2-SiO2 into dispersed single Pt atoms stabilized by metallic Ti, as shown by CO DRIFTS and in-situ EXAFS. The carbonyl peak on Pt NPs becomes symmetrical and narrower after particle disaggregation by CO, and the coordination number of Pt changes from 7 with Pt to ~3 with Ti. The Pt atoms interact with the neighboring Ti strongly to form PtTi alloys, which show very good stability (no obvious deactivation during more than 10h test at 550 °C) and high selectivity (~97%) to propylene in PDH. This is greatly improved from the base case of Pt/SiO2 which showed 37% loss of activity in a 3 h-long test and a maximum selectivity of 78% propene under the same conditions. Kinetics and structural and mechanistic investigations will be presented. Our work shows a facile novel way to prepare stable compositions of single atom alloys with distinct activity and selectivity.

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