Probing the surface of promoted CuO-Cr2O3-Fe2O3 catalysts during CO2 activation

The influence of basic oxide promoters on copper-chromium-iron oxide catalysts was investigated to determine the nature of surface oxygen species and structure-activity relationship for the reverse water-gas shift reaction. The catalysts were characterized with in situ XRD, in situ Raman, in situ XPS, in situ HS-LEIS and H-2-TPR. Two surface oxygen sites with different reduction characteristics were found to be present. The overall CO2 activation rate was found to correlate with both the number and reducibility of the more active oxygen species that were likely associated with the Cu-FeOx interfacial regions for enhanced hydrogen spillover. While addition of K2O somewhat preserved the interfacial regions and facilitated the reduction kinetics of surface oxygen, both Na2O and CaO significantly suppressed the availability of metallic Cu as well as the Cu-FeOx interfaces, leading to decreased reactivity. These findings provide a direction to promote the copper-iron catalysts by creating more metal-metal oxide interfacial sites.