Modulation Of Surface Structure Of Cerium Oxides And Their Catalytic Oxidation Performance

Phenolics are used as raw materials for various manufacturing industries.they would cause a serious damage to water resources if they are discharged without treatment.Deeply remove is needed because of the increasingly requirements of environmental protection.Catalytic wet air oxidation(CWAO)is an effective method to treat VOCs.VOCs can be decomposed into non-hazardous substances such as CO2,H2 O and NO2 by the catalytic method at a certain temperature and pressure.In many CWAO catalytic materials,cerium oxides often show good catalytic oxidation performance because of their reversible conversion of Ce3+/Ce4+.However,the requirements of environmental protection have become more strictly and the deep purification of VOCs is imperative.Therefore,in this work,the surface structure of the cerium oxides will be designed,and the relation of the structure of the cerium oxides and the catalytic oxidation performance of phenol will also be systematically studied to further improve the catalytic oxidation performance of the cerium oxide catalysts.The morphology modulation of CeO2 and thier catalytic performance were studied.Based on the one-step hydrothermal method,three kinds of morphologies were successfully prepared by adjusting the p H and the temperature.Studies showed that rod CeO2 can be prepared at the low temperature and low concentratiosn of sodium hydroxide,cube CeO2 can be prepared at high temperature and high concentratiosn of sodium hydroxide while the preparatiosn of octahedral CeO2 can be achieved with the help of a trace of sodium phosphate.TPR and N2 adsorption-desorption analysis revealed that the rod CeO2 has relatively high reduction temperature and relatively small specific surface area.XPS analysis showed that the rod CeO2 has the highest ratios of Ce3+/Ce4+ and Oads/Olatt.The catalytic performance studies showed that the rod CeO2 have the best degradation efficiency of phenol,indicating that the increase of the ratios of Ce3+/Ce4+ and Oads/Olatt can improve the catalytic oxidation performance of CeO2.The effects of heat treatment conditions on the ratios of Ce3+/Ce4+ and Oads/Olatt were studied.In order to further improve the ratios of Ce3+/Ce4+ and Oads/Olatt,the effects of calcination temperature and atmosphere were investigated.The results showed that low-temperature calcinations can improve the the ratios of Ce3+/Ce4+ and Oads/Olatt.Among the argon,nitrogen and air atmospheres,argon atmosphere is beneficial to improve the ratios of Ce3+/Ce4+ and Oads/Olatt.The catalytic performance studies showed that the CeO2 prepared by calcining at low temperature in argon atmosphere has the highest degradation efficiency,indicating that the heat treatment can achieve the surface modification of Ce3+/Ce4+ and Oads/Olatt and improve the catalytic performance.The effects of the introduction of zirconium on the ratios of Ce3+/Ce4+ and Oads/Olatt were studied.In order to further improve the ratios of Ce3+/Ce4+ and Oads/Olatt,four methods for introducting zirconium such as loading,sol-gel method,co-precipitation method and mechanical milling method were studied.Co-precipitation method showed the most obvious increase for the ratios of Ce3+/Ce4+ and Oads/Olatt.The effects of different temperatures and different precipitants were examined by the co-precipitation method.Studies showed that when ammonia and sodium hydroxide were used as precipitants,low temperatures are favorable for increasing the ratios of Ce3+/Ce4+ and Oads/Olatt,while ammonium bicarbonate was used as precipitants,the situation is opposite.The catalytic performance studies showed that the introduction of zirconium can significantly improve the ratios of Ce3+/Ce4+ and Oads/Olatt,especially when use sodium hydroxide as precipitant,the ratios of Ce3+/Ce4+ and Oads/Olatt can be effectively increased and the catalytic oxidation degradation of phenol can be improved.