Oxygen Vacancy-rich Porous Co₃O₄ Nanosheets toward Boosted NO Reduction by CO and CO Oxidation: Insights into the Structure–Activity Relationship and Performance Enhancement Mechanism

Abstract

Oxygen vacancy-rich porous Co 3 O 4 nanosheets (OV-Co 3 O 4 ) with diverse surface oxygen vacancy contents were synthesized via facile surface reduction and applied to NO reduction by CO and CO oxidation. The structure−activity relationship between surface oxygen vacancies and catalytic performance was systematically investigated. By combining Raman, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and O 2 -temperature programmed desorption, it was found that the efficient surface reduction leads to the presence of more surface oxygen vacancies and thus distinctly enhance the surface oxygen amount and mobility of OV-Co 3 O 4 . The electron transfer towards Co sites was promoted by surface oxygen vacancies with higher content. Compared with the pristine porous Co 3 O 4 nanosheets, the presence of more surface oxygen vacancies is beneficial for the catalytic performance enhancement for NO reduction by CO and CO oxidation. The OV-Co 3 O 4 obtained in 0.05 mol L −1 NaBH 4 solution (Co 3 O 4 -0.05) exhibited the best catalytic activity, achieving 100% NO conversion at 175 °C in NO reduction by CO and 100% CO conversion at 100 °C in CO oxidation, respectively. Co 3 O 4 -0.05 exhibited outstanding catalytic stability and resistance to high gas hour space velocity in both reactions. Combining in situ DRIFTS results, the enhanced performance of OV-Co 3 O 4 for NO reduction by CO should be attributed to the promoted formation and transformation of dinitrosyl species and −NCO species at lower and higher temperatures. The enhanced performance of OV-Co 3 O 4 for CO oxidation is due to the promotion of oxygen activation ability, surface oxygen mobility, as well as the enhanced CO 2 desorption ability. The results indicate that the direct regulation of surface oxygen vacancies could be an efficient way to evidently enhance the catalytic performance for NO reduction by CO and CO oxidation.

The Effect of Co Incorporation on the CO Oxidation Activity of LaFe1−xCoxO3 Perovskites

“…Depending on the conditions of the experiment, one or the other could be dominant, but neither could be ruled out. In the case of the herein studied perovskite catalysts, it is reasonable to assume that the formation of carbonate is mainly due to the surface reaction of CO with the two active O − , as reported for Co 3 O 4 catalysts [58]. The positive correlation of the extent of the reaction with the Co content can be qualitatively inferred by the gas phase CO and CO 2 intensities.…”

Single Ir Atoms Anchored on Ordered Mesoporous WO3 Are Highly Efficient for the Selective Catalytic Reduction of NO with CO under Oxygen‐rich Conditions

“…Thus the reduction of m‐WO 3 became easier, as confirmed by the H 2 ‐TPR analysis (Figure 6), which promoted the generation of oxygen vacancies. It has been revealed by the previous studies that the oxygen vacancies could serve as adsorption sites to capture the dissociated O* atoms by NO, which is well confirmed by the lower concentration of dissociated O* atoms on Ir 1 /m‐WO 3 , as shown in Figure 9c, and the role of CO is to combine the O* atom to form CO 2 and regenerate the oxygen vacancies [24,48,49] . Based on the above experimental results and analysis, we thus propose the catalytic reaction mechanism, which is illustrated in Figure 12.…”

Dynamic Surface Chemistry of Catalysts in Oxygen Evolution Reaction

“…This change can produce lattice molecular vibrational level changes, which give rise to Raman shifts. [ 58 ] XAS characterization is adopted to study the local geometric configurational changes and electronic structures of solids. For example, Xiao et al used XAS technique to detect oxygen vacancies by probing the lower coordination number of cobalt.…”