Ni/LnOx Catalysts (Ln=La, Ce or Pr) for CO₂ Methanation

Abstract

Abstract The effect of the LnOx support has been studied for Ni‐based CO 2 methanation catalysts. 10 wt.% nickel catalysts with LaOx, CeO 2 and PrOx supports have been prepared, characterized by N 2 adsorption, XRD, XRF, TG‐MS (N 2 ‐TPD and H 2 ‐TPR) and XPS, and have been tested for CO 2 methanation. The catalytic activity follows the trend Ni/CeO 2 >Ni/PrOx≫Ni/LaOx, all catalysts being very selective towards CH 4 formation. The activity depends both on the nature of the catalytic active sites and on the stability of the surface CO 2 and H 2 O species. Ni/CeO 2 is the most active catalyst because (i) the Ni 2+ ‐ceria interaction leads to the formation of the highest population of active sites for CO 2 dissociation, (ii) the reduced Ni 0 sites where H 2 dissociation takes place are the most electronegative and active, and (iii) the stability of surface CO 2 and H 2 O species is lowest. Ni/LaOx achieves lower activity because of the strong chemisorption of H 2 O and CO 2 , which poison the catalyst surface, and because this support is not able to promote the formation of highly active sites for CO 2 and H 2 dissociation. The behavior of Ni/PrOx is intermediate, being slightly lower to that of Ni/CeO 2 because the formation of active sites is not so efficient and because the stability of chemisorbed CO 2 is slightly higher.