Effect of cation–oligomer interactions on the size and reducibility of NiO particles on NiRu/SiO2catalysts

Abstract

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 (∼6 nm) that closely contact with RuO₂ particles, while the PEG-free process forms large NiO particles (∼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 (∼11 nm) on the PEG-additive-derived NiRu/SiO₂-CP catalyst, in contrast to NiRu/SiO₂-C (∼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.