Decomposition Of Ozone By Silver Supported On Different Supports

In recent years,the problem of ozone pollution has increasingly drawn people’s attention.Outdoors,the photochemical reaction of VOCs and NOx in the atmosphere produces ozone,which leads to excessive ozone concentrations in the surface troposphere.Indoors,ionization type air cleaners,printers and copiers can release ozone.Excessive ozone not only seriously threatens people’s health,cause skin,respiratory system,cardiovascular and cerebrovascular diseases,but also reduces crop yields.Thus,remove excessive ozone will be benefit to our health and eco-environment.Catalytic decomposition is considered to be the most efficient,safe and economical method.Ag-based catalysts can effectively improve the water resistance and with great ozone decomposition performance.It has reported that the type of supports in supported Ag-based catalysts has an effect on ozone decomposition.However,there have no systematic studies been done about how the support could influence the state of silver and then have an impact on the activity of catalysts.In this work,we successfully synthesized a series of catalysts by the impregnation method with kinds of metal oxides supports and different Ag content(1%,2%,4%,6%,8%,10%).Through the activity testing,it is found that the supported of silver has the most significant promoting effect on nanoAl2O3 and nano-Fe2O3 supports.So the study mainly focuses on Ag/Al2O3 and Ag/Fe2O3 two series of catalysts.In the study of Ag/Al2O3,Ag/nano-Al2O3 and Ag/AlOOH-900 two series of catalysts with different Ag content were synthesized.After activity testing,10%Ag/nano-Al2O3 had the best ozone removal ability at 30℃ under the conditions of c(O3)=40 ppm and RH=65%with the SV=840 L/(g·h).The activity of 10%Ag/nano-Al2O3 was up to 90%and remained stable.However,10%Ag/AlOOH-900 only exhibited 45%ozone conversion.The character results show that Ag nanoparticles were the active sites for ozone decomposition.There were lot of terminal hydroxyls on the surface of nano-Al2O3,which was 2.5 times of that of AlOOH-900.Abundant terminal hydroxyl groups led to high dispersion of Ag nanoparticles on the surface of nano-Al2O3 and increased the number of active sites to improve the performance of the catalysts.Besides,10%Ag/nano-Al2O3 had more metallic state Ag particles which was more superior active site for ozone decomposition and that the abundant terminal hydroxyl groups on nano-Al2O3 led to high dispersion of Ag kept in metallic state.In the study of Ag/Fe2O3,Ag/nano-Fe2O3 and Ag/usu-Fe2O3 two series of catalysts with different Ag content were synthesized.After activity testing,Ag/nano-Fe2O3 had the best ozone removal ability at room temperature under the same conditions as the previous paragraph.After 6 h,the activity of 4%Ag/nano-Fe2O3 was up to 68%.However,the ozone decomposition conversion of 4%Ag/usu-Fe2O3 was nearly zero.The character results show that there were abundant terminal hydroxyls and doubly bridging hydroxyls on the surface of nano-Fe2O3 and the content of hydroxyls on usu-Fe2O3 was less than nano-Fe2O3.Terminal hydroxyl groups and doubly bridging hydroxyl groups may be the anchoring sites of Ag species,so the silver species of 4%Ag/nanoFe2O3 were well dispersed.Besides,the abundant hydroxyl groups lead to form Ag-O-Fe structure on the surface of supports,which made the catalyst with high stability,so that 4%Ag/nano-Fe2O3 was better for ozone decomposition.The study of two catalysts systems reflect that the hydroxyl groups on the oxide surface are very important in the supported precious metal catalysts,which will be helpful to guide the design of more efficient supported silver catalyst for ozone decomposition.