High-temperature water-gas shift reaction over Ni/xK/CeO2 catalysts: Suppression of methanation via formation of bridging carbonyls

The effect of potassium (K) loading on ceria-supported nickel (Ni/xK/CeO2) catalysts on the water-gas shift reaction has been investigated. An optimum loading of 5 wt.% K was found to enhance the catalytic performance in terms of activity and selectivity. As evidenced by DRIFTS, the methane-suppressing effect of K is attributed to inhibition of the formation of nickel subcarbonyl species through interaction of Ni and K, coupled with strong adsorption of carbon monoxide (CO) on Ni via the formation of bridging carbonyls. Additionally, K was found to enhance reduction of CeO2 via}CANES and promote water dissociation on reduced CeO2 to form hydroxyl (OH) groups, which dissociate further into adsorbed oxygen that reacts with adsorbed CO on Ni to form adsorbed carbon dioxide (CO2). A dual-site redox mechanism was proposed and a good fit of the kinetic data with R-2 = 0.91 was obtained with the proposed kinetic model. (C) 2015 Elsevier Inc. All rights reserved.