Highly Active Ni/xNa/CeO2 Catalyst for the Water Gas Shift Reaction: Effect of Sodium on Methane Suppression

The effect of Na loading on the water gas shift (WGS) activity of Ni/xNa/Ce02 (with x = 0, 0.5, 1, 2, 5, and 10 wt %) catalysts has been investigated. Ni/2Na/Ce02 exhibited the highest performance in terms of WGS activity and methane suppression. Through H-2-TPR and XRD, the solubility limit of Na+ in Ce02 was found to be 2 wt %. At low loadings of Na (0.5 to 2 wt 96), Na+ was incorporated into the Ce02 lattice, generating a lattice strain and activating the lattice 02, thereby increasing the reducibility of the catalyst. However, beyond the solubility limit of 2 wt %, Na deposited on the Ce02 surface, retarding the reducibility of the catalyst. XPS spectra reveal greater surface concentration of adsorbed oxygen species with the introduction of Na. This can be attributed to the generation of more oxide vacancies for oxygen adsorption due to Na substitution into the ceria lattice. By in situ DRIFTS, methanation was found to be inhibited by the interaction between Na and Ni, leading to the absence of subcarbonyl species which are responsible for this undesirable side reaction. KEYWORDS: water gas shift, nickel catalyst, ceria, sodium, DRIFTS