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

• Potassium suppresses methanation by enhancing CO adsorption on Ni via forming bridging carbonyls.
• Water dissociation on CeO2 is enhanced by potassium which increases water affinity to the support.
• Increased density of OH groups on K-doped CeO2 support promotes WGS activity.
• WGS activity proceeds via dual-site redox mechanism on Ni/5K/CeO2 catalyst.

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 XANES 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 R2 = 0.91 was obtained with the proposed kinetic model.

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