Barium promoted Ni/Sm2O3 catalysts for enhanced CO2 methanation

Abstract

Low temperature CO₂ methanation is a favorable pathway to achieve high selectivity to methane while increasing the stability of the catalysts. A Ba promoted Ni/Sm₂O₃ catalyst was investigated for CO₂ methanation at atmospheric pressure with the temperature ranging from 200–450 °C. 5Ni–5Ba/Sm₂O₃ showed significant enhancement of CO₂ conversion particularly at temperatures ≤ 300 °C compared to Ni/Sm₂O₃. Incorporation of Ba into 5Ni/Sm₂O₃ improved the basicity of the catalysts and transformed the morphology of Sm₂O₃ from random structure into uniform groundnut shape nanoparticles. The uniformity of Sm₂O₃ created interparticle porosity that may be responsible for efficient heat transfer during a long catalytic reaction. Ba is also postulated to catalyze oxygen vacancy formation on Sm₂O₃ under a reducing environment presumably via isomorphic substitution. The disappearance of a high temperature (∼600 °C) reduction peak in H₂-TPR analysis revealed the reducibility of NiO following impregnation with Ba. However, further increasing the Ba loading to 15% formed BaNiO₃–BaNiO_2.36 phases which consequently reduced the activity of the Ni–Ba/Sm₂O₃ catalyst at low temperature. Ni was suggested to segregate from BaNiO₃–BaNiO_2.36 at high temperature thus exhibiting comparable activity with Ni/Sm₂O₃ at 450 °C.