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

The doping of In 2 O 3 significantly promoted the catalytic performance of Co 3 O 4 for CO oxidation. The activities of In 2 O 3 –Co 3 O 4 increased with an increase in In 2 O 3 content, in the form of a volcano curve. Twenty-five wt % In 2 O 3 –Co 3 O 4 (25 InCo) showed the highest CO oxidation activity, which could completely convert CO to CO 2 at a temperature as low as −105 °C, whereas it was only −40 °C over pure Co 3 O 4 . The doping of In 2 O 3 induced the expansion of the unit cell and structural distortion of Co 3 O 4, 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 O 2– to Co 3+ /Co 2+ became easier and implied that the bond strength of Co–O was weakened, which promoted the activation of oxygen. Low-temperature H 2 -TPR and O 2 -TPD results also revealed that In 2 O 3 –Co 3 O 4 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 CO 2 and obviously inhibited the accumulation of surface carbonate species. In short, the doping of In 2 O 3 induced the structural defects, modified the surface electronic structure, and promoted the redox ability of Co 3 O 4, which tuned the adsorption strength of CO and oxygen activation simultaneously.