Modification Of δ-MnO₂ For Catalytic Ozone Oxidation Of Toluene

Volatile organic compounds（VOCs）are important pollutants in air pollution.Due to the low reaction temperature and low energy consumption of the catalytic ozonation method,the research group used this to study the catalytic activity ofδ-MnO₂for the catalytic ozone oxidation of toluene.In order to improve the performance of the catalyst,this paper intends to modify theδ-MnO₂catalyst.A series of different metal M（M=Co,Cu,Fe,Cr,Zr,La,Ce,Ni,Ti,Zn,Al）modifiedδ-MnO₂catalysts were prepared by hydrothermal method,which were used to catalyze the ozonation of toluene.The evaluation criteria were toluene degradation rate,toluene mineralization rate,ozone removal rate and CO₂selectivity.The optimal single metal modification category and optimal ratio were obtained,and the catalyst was characterized by materials.The results show that:among the modified metals,Ni was the most modified,which doubles the activity of catalytic ozone oxidation toluene;suitable specific surface area,specific crystal form,more low-valence manganese content and adsorbed oxygen content and more strong redox was the reason for its stronger ability to degrade toluene.After comparing bimetal modification and metal ratio optimization,it was found that the effect of single metal modification was the best,and the optimal molar ratio of Ni to Mn was Ni:Mn=1:2.Investigating the influence of reaction conditions in the experiment found that:at room temperature,increasing the ozone concentration was conducive to the degradation of toluene;The increase of the initial concentration and space velocity of toluene would reduce the degradation rate of toluene;water vapor was not conducive to the degradation of toluene,but it could increase the mineralization of toluene;under certain conditions,the degradation rate of toluene by the catalyst could reach 95.1%,the mineralization rate could reach 23.4%,and the ozone removal rate could reach 100%.After long-term operation of the catalyst,the activity of the catalyst could be maintained for 24 h.After 2 hours of ozone regeneration in situ,the activity of the catalyst could be restored.Through activation energy calculation and reaction kinetics fitting,the catalyst Ni/δ-MnO₂could effectively reduce the activation energy of the reaction,and the degradation of toluene and ozone,and CO/CO₂formation were all pseudo first-order kinetics.It used gas-mass spectrometry（GC-MS）to analyze catalyst surface products and reaction outlet gas composition.Under the action of the catalyst Ni/δ-MnO₂,the intermediate products of catalytic ozone oxidation toluene are benzoic acid,benzyl alcohol,benzaldehyde,esters with benzene ring and ring-opened alkanes,which can be finally converted into CO/CO₂.Finally,a path for the catalyst Ni/δ-MnO₂ to degrade toluene was proposed.