Catalytic Decomposition Of Ozone Over P-type Metal Oxide And Humidity Resistance Study

Ozone is recognized as one of the critical air pollutants and can bring out detrimental effects on public health and living environment.Catalytic decomposition is an efficient and economical approach to remove ozone at low temperature.The active components of catalytic materials include some costly noble metals and some more commonly used transition metal oxides.However,the generally used transition metal oxides tend to be inactivated in the presence of water vapor,which limits their extensively application.Therefore,it is still necessary to explore ozone decomposition catalysts with facile synthesis method,low cost,highly active and high humidity resistance.P type metal oxides have been proved to facilitate the desorption of intermediates during ozone decomposition,resulting in superior catalytic removal performance of ozone compared with n type metal oxides.In this dissertation,several p type metal oxides(LaFe-based perovskite,nickel oxide,cuprous oxide and their derived catalysts)are successfully prepared and tested for ozone decomposition.The connection between inherent physical-chemical properties and catalytic capability are investigated.Specifically,some works have been done to explore humidity resistance mechanism.The main contents and results are listed below:(1)Perovskite LaFe03 based catalysts for efficient ozone catalytic decomposition and humidity resistance studyStoichiometric,nonstoichiometric and transition metal(Mn,Ni)doped LaFeO3 are prepared through sol-gel method and tested for ozone decomposition.Conversion is only 25%for 200 ppm ozone over conventional transition metal oxide Fe2O3 at high relative humidity(RH)90%,however,ozone conversion is still 85%over LaFeO3.Furthermore,5%mol Ni doped LaFeO3 further enhances humidity resistance with 93%conversion efficiency for 1000 ppm O3 at RH 90%.Characterization results suggest that water vapor can desorb easier form these perovskite materials at high RH.In addition,in-situ Raman spectra reveal that Fe2O3 becomes disordered in O3 decomposition process at high RH and intermediate O22-gathers at Fe2O3 surface,leading depression of catalytic activity.In contrast,LaFe03 and LaFe0.95Ni0.05O3 show neither deformation nor O22-accumulation at high RH,which is responsible for its strong activity.(2)Heterostructured Ni/NiO composite for ozone catalytic removal under high humidityPure NiO and Ni/NiO heterogeneous catalysts are simply synthesized using citric sol-gel method,the Ni/NiO heterogeneous structure can be adjusted by pH value in synthesis process.Ozone catalytic decomposition results show that Ni/NiO heterogeneous structure could promote ozone conversion at high relative humidity levels.Specificly,the conversion of 1000 ppm ozone over Ni/NiO composite could be as high as 98%at RH 90%after 8 h test,which is almost twice that of pure NiO.The excellent performance and high humidity resistance of Ni/NiO can be ascribed to the interaction between the metallic Ni and NiO,which could modify the surface valence,reducibility,oxygen mobility and desorption behavior of water on its surface.Chemiluminescence(CL)is used to supply some kinetic information of ozone decomposition over catalyst in dry and humid conditions.Ni/NiO foam monolithic catalyst with low pressure drop and flexible operation for ozone decomposition is fabricated to eliminate low-concentration ozone,which is an exploratory work.(3)Cu2O with different morphologies and different compositions for ozone catalytic decomposition Cu2O with different shapes and different compositions are synthesized through simple reductive solution chemistry route.Ozone decomposition test shows that(100)plane exposed cubic Cu2O exhibits higher catalytic activity than(111)plane exposed octahedral Cu20.Cu2O-CuO-Cu(OH)2 and Cu2O/rGO composite catalysts are further tailored to obtain higher ozone catalytic activity.The structure formation mechanism of Cu2O-CuO-Cu(OH)2 could be attributed to the synergistic reaction of the oxidation etching and acidic etching.The obtained Cu2O-CuO-Cu(OH)2 hierarchical nanostructure exhibits higher ozone decomposition efficiency than pure octahedral Cu2O.The excellent performance can be contributed to the stronger electron acceptance property and Cu+-Cu2+ redox couple.In-situ synthesized Cu2O/rGO exhibits much better performance for ozone decomposition than pure cubic Cu2O.The high performance can be attributed to the highly active ultrafine Cu2O nanoparticles(-3 nm)heterogeneously nucleated on rGO,which can promote electron density transfer and desorption of intermediate oxygen species during ozone decomposition process.(4)Cubic Cu2O with different sizes for ozone decomposition and application exploration of highly efficient ultra-fine Cu2OCubic Cu2O with particle size ranging from 40 nm to 1000 nm are synthesized by facile reduction method in aqueous solution at ambient condition.40 nm cubic Cu2O exhibits high room and low temperature activity,high moisture resistance and long-time stability for ozone decomposition due to the easy desorption of intermediate O22-from the surface of cubic Cu2O with small size.Scale up production of the preferred Cu2O with small size,a large-scale of fine Cu2O nanoparticles with a production of above 20 grams is achieved and the obtained Cu2O with several nanometers exhibits significant performance for removing high concentration and high humidity ozone.The ozone conversion efficiency is still above 95%for 3000 ppm ozone at RH 90%after 8 h running.Finally,the highly active Cu2O combined with Al honeycomb is used as monolithic catalyst to eliminate low level ozone,which shows great potential for applications.