A comparative study of nanosized IB/ceria catalysts for low-temperature water-gas shift reaction

The water-gas shift (WGS) activity of different M/ceria catalysts, where M is a metal from IB group (i.e. Au, Ag, Cu) has been studied. Two different techniques were used for the preparation of the catalysts—deposition–precipitation and a modified version of deposition–precipitation. HRTEM combined with EDS, X-ray diffraction, FT-IR of the molecules involved in the WGS reaction at 90 and 300 K as well as of forward and reverse WGS reaction up to 573 K, XPS and H2-TPR were employed to obtain information about the effect of different synthesis procedures on the surface and on the bulk structure of the catalysts and to explain the differences observed in the catalytic activity. The influence of each IB metal on the WGS activity has been investigated, too. The experimental results revealed that deposition–precipitation is the preferred method for preparation of active ceria-based catalysts because it allowed most part of IB metal promoters to be exposed at the catalyst surface. WGS reaction proceeds at the boundary between nanosized metallic particles and ceria, where CO adsorption on IB metals and H2O dissociation on oxygen-vacancy defects of ceria take place. The role of formate species as intermediates in the WGS reaction is confirmed by FT-IR spectroscopy. The correlation between the stability of formates and the WGS activity suggests that the decomposition of formates is a rate-limiting step.