Preparation Of Mn-Ti Composite Oxide Catalysts And Mechanism Studies For Photothermocatalysis VOCs And NO

Volatile organic compounds（VOCs）are one of the important precursors that lead to a series of environmental problems,such as photochemical smog.As the highest proportion of a class of pollutants in NO_x,nitric oxide（NO）can also cause photochemical smog,acid rain,greenhouse effect,and so on.Both of them have adverse effects of environment and human health.The photothermocatalysis synergistic reaction is the combination of photocatalysis and thermocatalysis,and the synergistic effect generated can be utilized to further improve the catalytic performance and realize efficient treatment without secondary pollution.Mn O_x is widely used in the removal of VOCs and NO due to its high activity and stability,rich valence states,excellent oxygen storage capacity and environmental friendliness.In addition,TiO₂ is a substance which exhibits good photocatalytic activity under ultraviolet irradiation（UV-light）.Therefore,this paper took Mn O_x-TiO₂ catalysts for catalytic treatment of VOCs and NO under the photothermocatalysis synergistic effect as the research system.Toluene,ethyl acetate and NO were selected as target pollutants to evaluate the catalytic performance of the catalysts for different types of VOCs and NO more comprehensively.Firstly,the effects of morphology and structure differences on the catalytic performance of Mn O_x-TiO₂catalysts was investigated.Secondly,the catalyst performance was optimized by regulating the molar ratio of Mn to Ti.Finally,the catalytic performance of samples was further improved by doping Ce.The main contents and conclusions are as follows:1.In order to eliminate toluene and NO simultaneously,different morphologies of Mn O_x-TiO₂ catalysts were synthesized and applied to the photothermocatalysis synergistic system under UV light irradiation through different hydrothermal conditions.The obtained morphologies included 3D hierarchical sheet structure（C sample）,3D hierarchical sheet stacked microspheres（P sample）and 3D hierarchical sticks stacked microspheres（N sample）.Among all the samples,N samples with 3D hierarchical sticks stacked microspheres showed good catalytic activity for toluene and NO.At240℃,the conversion of toluene and NO reached 72%and 91%,respectively.Combined with the characterization analysis,the high catalytic performance might be related to the large specific surface area,more types of oxygen adsorbed on the surface,more oxygen vacancies,more types of hypervalent atoms and other factors of the 3D hierarchical sticks stacked microspheres of the catalyst.2.A series of catalysts with different molar ratios of manganese to titanium(n _Mn:n _Ti=40:15,n _Mn:n _Ti=40:30,n _Mn:n _Ti=40:40,n _Mn:n _Ti=40:50,n _Mn:n _Ti=40:60)were synthesized by the hydrothermal conditions of 3D hierarchical sticks stacked microspheres.And these catalysts were applied in the photothermocatalysis synergistic system under UV light irradiation to investigate the effects of the molar ratio of different active component on the catalytic performance of the samples.Among all the samples,the sample with n _Mn:n _Ti=40:40 exhibited the best catalytic activity,which exhibited74%NO conversion and 62%ethyl acetate degradation at 240℃,respectively.3.MnO_x-Ce O₂-TiO₂(n _Mn:n _Ti=40:40)catalysts were synthesized by coprecipitation method with different Ce doping concentration(n _Mn-Ti:n _Ce=1:0.25,n _Mn-Ti:n _Ce=1:0.5,n _Mn-Ti:n _Ce=1:1,n _Mn-Ti:n _Ce=1:2,n _Mn-Ti:n _Ce=1:3),and were applied to the photothermocatalysis synergistic system under UV light irradiation to study the effect of different Ce doping amount on catalytic performance.It could be found that the sample with n _Mn-Ti:n _Ce=1:1 presented the highest catalytic performance than other samples,and the conversion of ethyl acetate and NO reached 72%and 83%at 240℃.