Experimental and theoretical investigations into the activity and mechanism of the water–gas shift reaction catalyzed by Au nanoparticles supported on Zn–Al/Cr/Fe layered double hydroxides

Abstract

Water–gas shift reaction (WGSR) is an industrialized reaction with numerous applications concerning CO removal and H2 generation. Since this process is widely used and occurs at elevated temperatures, the development of high efficiency and stable catalysts for WGSR and investigating their catalytic mechanism is a hot topic. In this paper, we demonstrate Au nanoparticles supported on different layered double hydroxides (LDHs) as highly efficient and stable catalysts for WGSR. The incorporation of Au nanoparticles significantly decreases the activation energy and enhances the catalytic activity of LDHs for WGSR, with Au/ZnCr–LDHs exhibiting the best catalytic performance including: 79.4% CO conversion, 102.1 μmol gcat−1 s−1 of reaction rate, 1.01 s−1 TOF values and 41.7 kJ mol−1 of activation energy. TPR experiments suggest that the addition of Au alters the redox cycle on the surface of the catalyst, a key intermediary step involved in the catalytic process. In situ DRIFTS shows that the production of CO2 during WGSR involves the reaction between CO and adsorbed O, which comes from the dissociation of OH species and not the decomposition of formates. DFT calculations indicate that Au–based catalysts can effectively lower the energy barrier of the kinetically relevant step of H2O dissociation, which is the most probable reason for the enhancement of activity. The calculated activation barriers coincide with the experimentally measured values with the order of Au/ZnCr–LDHs<Au/ZnFe–LDHs<Au/ZnAl–LDHs<LDHs. Particularly, redox mechanism B has the lowest activation barriers which is the most potential reaction pathway and perfectly supports the in–situ DRIFTS results.