Promoting Effects of In₂O₃on Co₃O₄for CO Oxidation: Tuning O₂Activation and CO Adsorption Strength Simultaneously

Abstract

The doping of In2O3 significantly promoted the catalytic performance of Co3O4 for CO oxidation. The activities of In2O3–Co3O4 increased with an increase in In2O3 content, in the form of a volcano curve. Twenty-five wt % In2O3–Co3O4 (25 InCo) showed the highest CO oxidation activity, which could completely convert CO to CO2 at a temperature as low as −105 °C, whereas it was only −40 °C over pure Co3O4. The doping of In2O3 induced the expansion of the unit cell and structural distortion of Co3O4, which was confirmed by the slight elongation of the Co–O bond obtained from EXAFS data. The red shift of the UV–vis absorption illustrated that the electron transfer from O2– to Co3+/Co2+ became easier and implied that the bond strength of Co–O was weakened, which promoted the activation of oxygen. Low-temperature H2-TPR and O2-TPD results also revealed that In2O3–Co3O4 behaved with excellent redox ability. The XANES, XPS, XPS valence band, and FT-IR data exhibited that the CO adsorption strength became weaker due to the downshift of the d-band center, which correspondingly weakened the adsorption of CO2 and obviously inhibited the accumulation of surface carbonate species. In short, the doping of In2O3 induced the structural defects, modified the surface electronic structure, and promoted the redox ability of Co3O4, which tuned the adsorption strength of CO and oxygen activation simultaneously.