Preparation Of Transition Metal-based Catalyst And Study On Catalytic Ozonation Of Phenol

Phenol is a kind of pollutant with high toxicity and poor biodegradability,which has great damage and threat to the ecosystem and human health.It is imperative to find ways to treat phenol-containing wastewater.Heterogeneous catalytic ozonation combines the strong oxidation ability of ozone with the adsorption and catalytic performance of catalysts.It is a promising method for water treatment which can accelerate the reaction and improve the oxidation efficiency.In this work,three kinds of transition metal-based catalysts were prepared based on the high activity,good stability,easy separation and recovery of transition metal-based catalysts,and their catalytic efficiency,reaction kinetics,optimal experimental conditions,reaction mechanism and stability were investigated.The specific content is as follows:（1）Mn-Fe-Ce/Al₂O₃ ternary catalysts were prepared by co-impregnation and calcination.Catalytic ozonation of phenol showed that Mn-Fe-Ce/Al₂O₃ had high catalytic activity,and the removal rate of phenol could reach 87.97%after 30 min of reaction.Reuse experiments showed that the catalysts still had high catalytic activity after 5 cycles,and the surface groups did not change.The mechanism study showed that the direct oxidation of phenol by ozone and the indirect oxidation of phenol by hydroxyl radical（·OH）both existed in this system,and the·OH mechanism was dominant.The hydroxyl groups on the surface of the catalysts were the catalytic active sites,which could accelerate the decomposition of ozone to produce·OH.The redox cycles of the three transition metals accelerated the electron transfer of the whole reaction system.（2）Transition metal-based Metal-Organic Frameworks（MOF）catalysts Ni-Cu-MOF were prepared by mild solvothermal method for ozonation of phenol.The removal rate of phenol was 67.44%after 30 min of reaction.The optimum reaction conditions were as follows:the initial concentration of phenol was 300 mg L^-1,the dosage of catalysts was 1 g L^-1.Although Ni-Cu-MOF had high catalytic activity after five reactions under neutral conditions,it was not stable under strong alkaline conditions.The mechanism study showed that Lewis acid sites were the active centers which could reacted with ozone to produce highly active·OH for improving the removal rate of phenol.（3）A series of layered double hydroxide（LDHs）materials were prepared by co-precipitation method.The experimental results showed that Cu₄Al₂-LDH had little catalytic activity for the ozonation of phenol,but with the doping of Mn,Cu₄Mn_xAl_2-X-LDH performed good catalytic activity.The control-experiment results showed that Cu₄Mn₁Al₁-LDH had the highest catalytic efficiency and maintained good stability after five reuses,the removal rate of phenol was 66.36%after 30 min of reaction.By studying the correlation between Mn content and catalytic activity,it can be seen that Mn component is the active component of catalyst.The Mn²⁺-Mn³⁺-Mn⁴⁺redox cycle is responsible for electron transfer in the reaction,which plays a key role in the decomposition of ozone and the formation of·OH.