Effect of cation-oligomer interactions on the size and reducibility of NiO particles on NiRu/SiO2 catalysts

A NiRu/SiO2 catalyst was prepared by a new method. The presence of polyethylene glycol (PEG) molecules allows their oligomer groups to interact with the metallic ions in the liquid, which creates small NiO particles (similar to 6 nm) that closely contact with RuO2 particles, while the PEG-free process forms large NiO particles (similar to 11 nm) with separated RuO2 on SiO2 after calcination in air. The formation of close contacts between NiO and RuO2 particles improves the promotional efficiency of Ru. Therefore, small NiO particles can be reduced at lower temperature than that of large NiO particles on SiO2, a finding that contrasts with the dispersion-reducibility dependence inherent to the oxide-supported nickel-based catalyst. This leads to smaller Ni particles (similar to 11 nm) on the PEG-additive-derived NiRu/SiO2-CP catalyst, in contrast to NiRu/SiO2-C (similar to 28 nm) catalyst prepared by the PEG-free process. In the methanation reaction, the NiRu/SiO2-CP catalyst has a lower initial turnover frequency (TOF) per mole of surface Ni, however, it shows better long-term stability. Instead, as a result, the NiRu/SiO2-CP catalyst has a higher TOF after reaction for 30 h than the NiRu/SiO2-C catalyst, which deactivates due to the deposition of less reactive carbon species.