Tungsten as an interface agent leading to highly active and stable copper–ceria water gas shift catalyst

Abstract

A series of W–Cu–Ce mixed oxide catalysts prepared by microemulsion was evaluated in the water-gas shift (WGS) reaction. At low temperatures (<350°C), the total conversion of CO on the W–Cu–Ce systems was two times larger than on binary Cu–Ce mixed oxides which are well known catalysts for the WGS. In addition and in contrast with Cu–Ce, W–Cu–Ce catalysts were stable and no signs of deactivation were found after 10h of reaction time. The rationale for the excellent catalytic performance presented by the W–Cu–Ce ternary oxide was elucidated from the viewpoint of a complete structural (e.g. analysis of the long and short range order) and redox behavior characterization using in situ, time-resolved X-ray diffraction (XRD) as well as X-ray absorption (XAS), infrared (diffuse reflectance Fourier transform DRIFTS) and Raman spectroscopies. From a single phase fluorite-type structure, the catalysts show significant structure/redox evolution under reaction conditions as a function of the W and Cu content. As it occurs in the parent Cu–Ce system, the dominant presence of metallic Cu and fluorite-type oxide phases is detected under reaction conditions for the ternary systems. An outstanding promotion of catalytic properties is nevertheless evidenced for samples with W content above 10 at.% and is shown to be related to the presence of oxidized W–Cu local entities. Such local entities, which are obviously characteristic of the ternary system, greatly enhance fluorite redox properties and play an interfacial role between the main metallic Cu and fluorite-type oxide phases. As a consequence of all these effects, incorporation of W into the initial material leads to efficient WGS catalysts, most promising for their application in the so-called low temperature region, e.g. below 350°C.