Photocatalytic Ozonation Mechanism Investigation Of Gaseous Hexane Isomers On MO_x-TiO₂?M=Cu,Mn,Ag?

With the rapid development of China's industry,the problem of air pollution has become increasingly serious.Volatile Organic Compounds?VOCs?are an important class of atmospheric pollutants.They not only form secondary pollutants through photochemical reactions,but also are important precursors of fine particles.Most of them are carcinogenic to human body.Alkanes are a class of major VOCs and are important atmospheric pollutants emitted by the petrochemical industry.They are extremely harmful to the atmospheric environment,employed workers and surrounding residents.Therefore,how to effectively eliminate alkane VOCs pollution is currently the field of air pollution control in the petrochemical industry.Photocatalysis has a mild condition,normal temperature and pressure reaction,low energy consumption,energy saving and environmental protection advantages become the main technology for degrading alkane VOCs.Although the chemical method represented by TiO₂ photocatalysis technology can degrade most VOCs,its degradation efficiency for alkane VOCs is not very satisfactory.This is mainly because the bond energy of C-C and C-H in the alkane VOCs is relatively high,requiring more energy and a longer reaction time to break it.However,the removal efficiency of alkane VOCs needs to be improved.Therefore,in order to improve the purification efficiency of alkane VOCs,the photocatalytic oxidation of hexane isomers by photocatalytic ozonation using bimetallic oxide composite titanium dioxide as catalyst and hexane isomer as target pollutant.Furthermore,by exploring the relationship between free radicals and degradation products in the reaction system,combined with quantum chemical calculations,the similarities and differences of the photocatalytic ozonation mechanism of hexane isomers were elucidated.The main research carried out is as follows:?1?Nanocomposites of MOx–TiO₂?M=Cu,Mn,Ag?supported on foam nickel?MOx/TiFN?were successfully applied in the photocatalytic ozonation of gaseous alkane.All MOx samples presented nanoflake structures with two metal oxides,corresponding to Cu₂O and CuO in CuOx,Mn₂O₃ and MnO₂ in MnOx,and Ag and Ag₂O in AgOx.These binary metal oxides composited with TiFN displayed 1.3 to 2.0 times higher degradation and mineralization efficiencies toward 350 ppmv of n-hexane than TiFN.The promoted?OH and?O₂^-from O₃ conversion on MOx were responsible for the enhanced efficiency.And?O₂^-made a higher contribution to the enhancement,since the relative amount of?O₂^-increased by 3.2 to 7.9 times more than?OH after MOx composition.Our experimental and theoretical mechanism results further confirmed that both?OH and?O₂^-were important for the epoxidation transformation of n-hexane on MOx/TiFN,while?OH dominated in the conversion of alcohol intermediates to corresponding radicals,and?O₂^-determined the subsequent epoxidation transformations of these radicals to four epoxides with 3,5 and 6membered rings.The present work could provide deep insight into an enhanced mechanism for nanomaterial photocatalytic ozonation technology,and efficiently replenish alkane atmospheric transformation mechanisms.?2?The best active Cu₂O-CuO/TiO₂ composites in Chapter 2 were selected as catalysts,and three hexane isomers were further developed.Degradation efficiency and mechanism of dimethylbutane).The results show that the Cu₂O-CuO/TiO₂ catalyst is equivalent to three hexane isomers in a degradation time of 360 min after containing 160 ppm ozone.All three hexane isomers exhibit high degradation efficiency and stability.Among them,3-methylpentane has the best degradation efficiency and can reach about 90%.Through product detection and infrared characterization of the catalyst,it was found that the2-methylpentane product had the largest number of products,including 11 products such as hexanol,ketone and 5-membered alicyclic ring,while 3-methylpentane only detected four kinds of products,Three hexanol and one pentad lactone ring.The reason for this is that the degradation efficiency of 2-methylpentane is lower than that of 3-methylpentane,so there are many intermediate products on the catalyst,3 methyl pentane has the best degradation efficiency lead to very few products on the catalyst.Through the results of different degradation time catalyst products,it was found that the five-membered cyclic products of the three isomers could be monitored after 360 minutes,indicating that the product is a cumulative process on the catalyst,when the amount of the product on the catalyst reaches a certain concentration.The cyclic product will be formed later.The degradation pathways of these three hexane isomers were inferred from the product list and the results of the previous chapter,effectively supplementing the atmospheric conversion mechanism of hexane isomers.