Identifying Size Effects of Pt as Single Atoms and Nanoparticles Supported on FeO_x 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 FeO_x-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 FeO_x 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.