Effect of Ca doping on the performance of CeO₂–NiO catalysts for CH₄ catalytic combustion

Methane catalytic combustion was carried out over the Ce_0.9–xNi_0.1Ca_xO_δ (0 < x ≤ 0.3) catalysts prepared by a citric acid complexation–combustion method. When x ≤ 0.1, the presence of Ca can enhance the surface area and reduce the crystalline size, and improve the reduction of the dispersed NiO species in catalyst, resulting in an improvement of the catalytic activity of Ce_0.9–xNi_0.1Ca_xO_δ. The XRD and Raman results show that Ce_0.9–xNi_0.1Ca_xO_δ (x ≤ 0.1) solid solution can form by Ni and Ca incorporation in the CeO₂ lattices. TEM and etching results reveal that part of Ni disperses well on the surface of Ca-doped sample. FT-IR testing shows that with an increase in Ca amount (x > 0.1), more carbonate species (mainly carbonate calcium) can form on the catalyst surface, which would severely debase the catalytic activity of Ce_0.9–xNi_0.1Ca_xO_δ.