Treatment Of Cresol Wastewater With MeZrO₃ Perovskite Catalytic Ozonation

As catalytic wet ozonation（CWOO）exhibited excellent capacity in the degradation of various biorefractory organic wastewater,it has been regarded as the one of the preferred technologies in the wastewater treatment.With the continuous in-depth research in CWOO,it was found that the insufficient stability of the CWOO catalysts was one of the major reasons restricting the industrial application of CWOO.In this study,based on the high stability of perovskite catalysts and high activity in catalytic oxidation reaction,the MeZrO₃ perovskite catalysts were applied into the CWOO.The effect of the preparation method of MeZrO₃ perovskite catalysts on CWOO reaction was investigated.The mechanism of its catalytic reaction was discussed.The main results were as follows.The CaZrO₃ perovskite catalysts were prepared by co-precipitation method,and the effects of aging temperature,mole ratio of calcium/zirconium and calcination temperature on the purity of CaZrO₃catalysts were studied.It was found that the purity of the prepared CaZrO₃catalyst was close to 100%under the conditions of aging temperature of100℃,mole ratio of calcium/zirconium 1.1:1 and calcination temperature of 1100℃.Based on the discussion above,the effects of calcination time,different PEG molecular weight and PEG dosage on the structure of CaZrO₃ catalysts and the catalytic performance of CWOO were discussed.The results showed that the TOC removal of the catalysts with the best performance in CWOO was about 2.9 times higher than that of the ozonation alone.The ozone utilization rate reached about 40% as for the optimal CaZrO₃ catalysts.In order to investigate the reaction mechanism of CaZrO₃ catalysts in ozonation,TEM,in-situ XRD,EPR and other characterization methods were used to analyze the structure of the catalysts and to detect the active radicals during the CWOO reaction.Furtherly,by means of density functional theory（DFT）,the catalytic mechanism of CaZrO₃ catalysts in CWOO was proposed.It has been proved that compared with the traditional ZrO₂ catalyst,the CaZrO₃ catalyst was more conducive to generate oxygen vacancies.Oxygen vacancies can catalyze ozone to generate superoxide and singlet oxygen.At the same time,ozone could also interact with hydroxyl groups on the catalyst surface to generate hydroxyl radicals.The generated reactive oxygen species could quickly react with the target pollutant m-cresol,thereby achieving the rapid degradation of pollutants.The catalyst with the best performance obtained did not decay in activity after 100 h of continuous reaction.The A-site of CaZrO₃ was substituted with Sr and Ba,respectively,to examine their activity in the reaction of CWOO to degrade m-cresol.Both catalysts also exhibited excellent oxidation activity in the CWOO reaction.Under the same conditions,the catalytic activities of the three catalysts in CWOO were:CaZrO₃>SrZrO₃>BaZrO₃.