Identifying Size Effects of Pt as Single Atoms and Nanoparticles Supported on FeOx for the Water-Gas Shift Reaction

Identification of size effects at an atomic level is essential for designing high-performance metal-based catalysts. Here, the performance of a series of FeOx-supported Pt catalysts with Pt as nanoparticles (Pt-NP) or single atoms (Pt-SAC) are compared for the low-temperature water-gas shift (WGS) reaction. A variety of characterization methods such as adsorption microcalorimetry, H2-TPR, in situ DRIFTS, and transient analysis of product tests were used to demonstrate that Pt nanoparticles exhibit much higher adsorption strength of CO; the adsorbed CO reacts with the OH groups, which are generated from activated H2O, to form intermediate formates that subsequently decompose to produce CO2 and H2 simultaneously. On the other hand, Pt single atoms promote the formation of oxygen vacancies on FeOx which dissociate H2O to H2 and adsorbed O that then combines with the weakly adsorbed CO on these Pt sites to produce CO2. The activation energy for the WGS reaction decreases with the downsizing of Pt species, and Pt-SAC possesses the lowest value of 33 kJ/mol. As a result, Pt-SAC exhibits 1 order of magnitude higher specific activity in comparison to Pt-NP. With a loading of only 0.05 wt % the Pt-SAC can achieve ～65% CO conversion at 300 °C, representing one of the most active catalysts reported so far