Dual Metal Active Sites in an Ir₁/FeO_xSingle‐Atom Catalyst: A Redox Mechanism for the Water‐Gas Shift Reaction

Abstract

Herein, we report a theoretical and experimental study of the water‐gas shift (WGS) reaction on Ir1/FeOx single‐atom catalysts. Water dissociates to OH* on the Ir1 single atom and H* on the first‐neighbour O atom bonded with a Fe site. The adsorbed CO on Ir1 reacts with another adjacent O atom to produce CO2, yielding an oxygen vacancy (Ovac). Then, the formation of H2 becomes feasible due to migration of H from adsorbed OH* toward Ir1 and its subsequent reaction with another H*. The interaction of Ir1 and the second‐neighbouring Fe species demonstrates a new WGS pathway featured by electron transfer at the active site from Fe3+−O⋅⋅⋅Ir2+−Ovac to Fe2+−Ovac⋅⋅⋅Ir3+−O with the involvement of Ovac. The redox mechanism for WGS reaction through a dual metal active site (DMAS) is different from the conventional associative mechanism with the formation of formate or carboxyl intermediates. The proposed new reaction mechanism is corroborated by the experimental results with Ir1/FeOx for sequential production of CO2 and H2.

Research Progress and Application of Single-Atom Catalysts: A Review

“…Liang et al [102] studied redox mechanism of Ir1/FeOx single-atom catalyst in watergas conversion (WGS) reactions. Water is readily decomposed into OH * on a single atom of IR1 and H * on a nearby O atom bonded to the Fe position.…”

Synthesis of High Metal Loading Single Atom Catalysts and Exploration of the Active Center Structure

“…For the characterization of SACs, CO is an ideal probe. The behavior of CO adsorption on a metal surface has been widely studied [177] . CO can form a linear adsorption geometry as well as a bridging adsorption geometry [178] .…”

“…The behavior of CO adsorption on a metal surface has been widely studied. [177] CO can form a linear adsorption geometry as well as a bridging adsorption geometry. [178] The bridging adsorption geometry requires two metal atoms, indicating the existence of metal NPs.…”

A Multitechnique Study of C2H4 Adsorption on Fe3O4(001)

“…In recent years, the field of “single-atom catalysis” (SAC) has emerged as an intensely studied topic in catalysis research, and iron oxides continue to be a common choice of support material. 4 − 10 Such catalysts are typically prepared by coprecipitation, and the support is nominally an Fe 2 O 3 powder. Nevertheless, it is often labeled FeO x to reflect that the oxide, and especially its surface, is reduced when the catalyst is activated by heating in CO or H 2 .…”