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

Abstract

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.

In Situ Dispersion of Palladium on TiO2 During Reverse Water–Gas Shift Reaction: Formation of Atomically Dispersed Palladium

“…[54,61] Aprior study using atomically dispersed Pt for WGS also evidenced the absence of formate,a lthough they erroneously concluded aredox mechanism. [62] Thefeatureless IR spectra illustrate that caution must be taken before concluding that intermediates observed via in situ spectroscopy are kinetically relevant. Thea bsence of carbonyl is consistent with CO desorption occurring at room temperature (Figure S9) and recent literature reports.…”

The Multifaceted Reactivity of Single‐Atom Heterogeneous Catalysts

“…[83] Through in-depth characterization an associative mechanism was suggested over NPs in which CO reacts with OH species generated by the activation of H 2 Oonthe support to form intermediate formates.I nc ontrast, ar edox mechanism occurs over the SAC. Nevertheless,asubsequent experimental comparison of Pt 1 /FeO x and Pt/FeO x catalysts by Chen et al further supported increased specific rates with decreasing atomic population.…”

Catalytic Semi‐Water–Gas Shift Reaction: A Simple Green Path to Formic Acid Fuel

“…In these cases, formiate is the most abundant experimentally observed intermediate because its formation barrier is lower than its dissociation barrier. However, it is difficult to desorb it from the catalyst surface . Ruthenium complexes supported in SILPs have also presented higher activation energies (41–84 kJ mol −1 ) in the WGSR .…”

“…However,i ti sd ifficult to desorb it from the catalyst surface. [56][57][58][59][60][61] Ruthenium complexes supported in SILPs have also presentedh igher activation energies (41-84 kJ mol À1 )i nt he WGSR. [31,32,62] Of note, neither of these catalytic systems were able to yield FA.…”