Catalytic Decomposition Of Gaseous Ozone Over Manganese-based Compounds

Long-term exposure to low-level ozone will damage human health.The safe,stable and efficient ozone removal issue is needed to be addressed urgently.The catalytic decomposition of ozone at room temperature is the most promising technology and the key lies in the development of catalysts with high activity.The rapid development in nanomaterial science and in-situ monitoring on the catalytic process have enable us to explore the the relationship between structure of manganese-based materials and ozone decomposition activity.This study aims to clarify the active sites of ozone decomposition over manganese oxides,which will provide new insight for the development of novel catalysts.We prepared MnO₂ with different crystal structures and morphologies and found that the catalytic activity of a-MnO₂ was better than that of b-MnO₂,g-MnO₂,the activity of nanofibers a-MnO₂ was better than that of nanorods,nanotubes a-MnO₂.The catalytic activity of MnO₂ strongly depended on the content and dispersion of oxygen vacancies.By adding a surfactant and dopant of low valence metal ions,we tried to tune the oxygen vacancy content and improve the catalytic activity.The results showed that the catalytic activity of obtained Fe³⁺ dopped MnO₂ is better than that of commercial ozone scrubber?Hopcalite?.In-situ Raman spectroscopy results showed that peroxide species formed during ozone decomposition reaction and the decomposition of peroxide species was the rate-limiting step.Considering the relationship between oxygen vacancy density and ozone decomposition activity,we proposed the ozone decomposition mechanism based on the involvement and recycling of oxygen vacancy.On the contrary,if the decomposition of peroxide species is not sufficiently fast,the oxygen vacancy site can't be recovered.The deactivation of catalyst can be attributed to oxygen vacancy being filled and/or surface being covered by water molecule and accordingly the regeneration strategy was proposed.After the deactivated catalyst was reduced at 200°C for 2h in the H2 atmosphere,its activity was regenerated,keeping the initial activity after 3 times recycling use.We also prepared submicron spherical MnCO₃ via coprecipitation at roomtemperature and found its good catalytic activity for ozone decomposition,which is better than that of nanofibres a-MnO₂.Furthmore,the powder catalyst was uniformly loaded onto the non-woven fabrics with low air resistance by using PTFE emulsion as adhesives via a simple and low-cost method,which is applicable for practical use.The ozone decomposition ratio of supported MnCO₃ was kept 100% after 8 d continuous reaction under the conditions of inlet ozone concentration 14 ppm,space velocity 42040 h-1 and relative humidity ¹%.