The promoting role of Ag in Ni-CeO₂ catalyzed CH₄-CO₂ dry reforming reaction

The catalytic performance of Ag promoted Ni/CeO₂ catalyst has been investigated in methane and carbon dioxide dry reforming reaction. The temperature-dependent catalytic activity and time-on-stream catalytic performance at 760°C under different feeding conditions have been explored. Pristine Ni/CeO₂ is not stable as a result of coke deposition and surface reconstruction. In addition, co-feeding of H₂ can adversely influence the long-term stability of Ni/CeO₂. Ag severely reduces the intrinsic catalytic activity of Ni/CeO₂ catalyst, while enhances the long-term stability by diminishing coke deposition. Ag is applicable as a promoter under various reaction conditions, from N₂ diluted feedstock to H₂ co-fed and carrier-gas free feedstock. Kinetic studies show that Ag elevates the activation energy from 91 to ca. 140kJ/mol by a loading of 0.3mol.%, excessive Ag loading does not affect activation energy. The role of Ag is to block step sites on Ni surface that is associated with carbon nucleation and growth, and to promote gasification of coke formed. Besides, Ag alters the type of coke formed over Ni surface from recalcitrant whisker/encapsulating carbon to easily gasifiable amorphous carbonaceous species.