Highly c-disordered birnessite with abundant out-of-layer oxygen vacancies for enhanced ozone catalytic decomposition

Ozone pollution has long been a hazard to human health and ecosystems. Manganese oxides have been intensively investigated for O-3 decomposition, but improving the catalytic activity and stability of MnOx remains challenging. Herein, hexagonal birnessites with varying degrees of c-disordering were synthesized and showed strikingly different catalytic activities. As the degree of c-disordering increase, the highly disordered birnessite (HDB) possessed the highest content of oxygen vacancies (V-O) and thus demonstrated the superior catalytic activity. The HDB remained a high O-3 conversion efficiency of 96% even after reaction for 24 h at a high space velocity of 600,000 mL center dot g(-1)center dot h(-1) and under the relative humidity of 50%. At the same time, HDB could be easily regenerated after heating for 1 h at 200 degrees C under air atmosphere. We found two different types of V-O (the in-layer V-O and the out-of-layer V-O) on the c-disordered birnessites, and the out-of-layer V-O was more stable than the in-layer V-O. The out-of-layer V-O was beneficial to desorption of the intermediate O-2(2-) and reduced the competitive adsorption of H2O, which accounted for the enhanced catalytic stability of HDB. This work may provide guidance for the V-O engineering in metal oxides toward the catalytic purification of waste gases.

Automated summary

Ozone pollution has long been a threat to human health and ecosystems. Researchers have synthesized hexagonal birnessites with varying degrees of c-disordering and found that the highly disordered birnessite (HDB) with the highest content of oxygen vacancies (V-O) demonstrated the superior catalytic activity. The HDB maintained a high O-3 conversion efficiency even after 24 hours of reaction at a high space velocity and under high humidity. The stability of HDB was attributed to the presence of stable out-of-layer V-O which facilitated the desorption of intermediate O-2(2-) and reduced the competitive adsorption of H2O.