Enhanced Methane Oxidation over Co<sub>3</sub>O<sub>4</sub>–In<sub>2</sub>O<sub>3</sub>-<i>x</i> Composite Oxide Nanoparticles via Controllable Substitution of Co<sup>3+</sup>/Co<sup>2+</sup> by In<sup>3+</sup> Ions
Yong Zheng, Chen Wang, Juanjuan Li, Fulan Zhong, Yihong Xiao, Lilong Jiang
Abstract
Composite oxide nanoparticles are promising candidates for catalytic applications to reduce the usage of expensive noble metals. However, the associated inferior low-temperature activity imposes major challenges on the rational design and modulation of compositions. Herein, we reported for the first time the successful synthesis of Co3O4–In2O3 composite oxides with the nanoparticle size of 10–20 nm for methane combustion via a modified precipitation method adopting the organic base N-butylamine as a precipitator to eliminate the negative effects resulting from conventional inorganic base precipitators. The doped In3+ would first occupy octahedral sites of the spinel Co3O4 and then tetrahedral sites, resulting in the increase of Co2+ ratio on the surface when the doped molar ratio (nIn) was 0–0.2 and decrease with excessive doping (nIn of 0.2–0.4). The increment of Co2+ ratio was essential for the formation of abundant reactive oxygen species, improvement of reducibility, and optimization of surface acidity, which synergistically contributed to superior catalytic activity with a T99 of 395 °C. The catalytic activity of the tailored Co–In-0.2 nanocatalyst is among the best of the state-of-the-art Co-based catalysts; meanwhile, it also exhibits excellent stability and water resistance.