Preparation Of CeCu Oxide Catalyst For CWPO Degradation Of Quinoline And Bisphenol A

With the development of modern industry,remarkable amount of organic pollutants has been discharged into water through the discharge of industrial wastewater or other ways.Those organic pollutants,which are hard to be biodegraded,pose a serious threat to human and environment.The quinoline and bisphenol A found in polluted water come from different sources and are structurally different.The study on the removal of quinoline and bisphenol A can provide the key points for the removal of nitrogen-containing heterocyclic compounds and endocrine disruptors,respectively.However,both quinoline and bisphenol A moleculars are characterized by high toxicity and refractory degradation,and thus are difficult to be treated by conventional biochemical methods.Therefore,to develop an efficient and reliable water treatment technology has become a hot topic in recent years.Catalytic wet peroxide oxidation?CWPO?is a promoting oxidation technology which can overcomes the shortcomings of traditional wet oxidation technology like high reaction temperature and operation pressure.Furthermore,H₂O₂ is used in CWPO processes as an oxidant instead of high pressure oxygen or air,and then the mass transfer resistance of reaction is reduced and the reaction rate is increased.In this thesis,new copper sulfate catalysts were developed based on the Fenton reaction system to catalyze the oxidative degradation of quinoline and bisphenol A.The new copper sulfate catalysts were studied in the homogeneous CWPO processes of simulated wastewater containing quinoline and bisphenol A under different reaction conditions.It has been found that the Cu²⁺catalyst can exhibit high catalytic oxidative degradation activity for either quinoline or bisphenol A.Unfortunately,the leaching of active components,which leads to secondary pollution,was also observed.The used catalysts were found to be inactive.In order to overcome the shortcomings of such Cu²⁺catalyst,CeCu oxide catalysts were prepared by citric acid complexation method using Cu²⁺as main active phase and Ce as assistant to achieve high activity,high stability.The CeCu oxide catalysts with different Cu/Ce molar ratio were prepared at different calcination temperatures by citric acid complexation method.The phase composition,surface morphology,reducibility,specific surface area,elemental composition and chemical valence of the CeCu catalysts were characterized.The effects of the catalysts preparation conditions on their catalytic performance were studied in heterogeneous CWPO processes while the relationship between different reaction conditions and heterogeneous CWPO reaction results was also investigated.The stability of the catalyst and the kinetics of heterogeneous CWPO reaction were also investigated to understand the degradation mechanism of the heterogeneous CWPO processes catalyzed by CeCu catalysts.The commonly used Fenton catalysts?e.g.,ferrous sulfate and ferric sulfate?are almost inactive for the degradation of quinoline and bisphenol A.In the catalytic oxidation degradation of quinoline and bisphenol A,the catalyst must be highly active,selective,and adaptable.Manganese sulfate was found to be inactive for the degradation of quinoline but active for bisphenol A.Copper acetate is active for the degradation of quinoline but almost inert for bisphenol A.The formation of CeCu solid solution was found in the CeCu oxide catalysts,which were prepared at high calcination at temperatures.The CeCu oxide catalysts have porous surface structure with CeO₂ and CuO as main surface species and little Cu₂O.The surface lattice oxygen is richer than adsorbed oxygen and hydroxyl oxygen in CeCu oxide cayalysts.The calcination temperature of catalyst exhibits a great influence on the activity and structural stability of the catalysts.At low calcination temperatures,the catalysts with poor catalytic activity were obtained due to low structural stability and the easy leaching of the active component.On th e contrary,very high calcination temperature easily leads to the sintering of catalysts and very weak interaction between CuO and CeO₂.The Cu/Ce molar ratio was found to show a great influence on the phase structure of the catalysts.As the Cu content increases,the reducibility of catalysts decreases.Therefore,the Cu/Ce molar ratio needs to be well tuned to obtain an appropriate interaction between Cu species and Ce species and then a good catalytic activity.When the Cu/Ce molar ratio is 1.0,in both the removal of quinoline and bisphenol A,the CeCu catalyst presents the highest activity attributed to the fact that the Cu species can be well dissolved into the CeO₂ lattice to form a solid solution,which has a large amount of active centers to participate in the activation of H₂O₂ molecules in the catalytic reaction.In the early stage of the CWPO reaction,more catalyst or H₂O₂ is conducive to the rapid progress of the CWPO reaction.The amount of catalyst and H₂O₂ shows little effect on reaction in its later stage.Higher reaction temperature can accelerate the degradation of quinoline and bisphenol A.Increasing the initial concentration of quinoline or bisphenol A will lead a lower removal effect in the early reaction stage,but a high removal rate can be achieved if the reaction time is long enough.Compared with homogeneous CWPO reaction,heterogeneous CWPO reaction can be carried out in a wider pH range?quinoline pH=3.8-10.5,bisphenol A,pH=1.6-7.9?due to the addition of Ce,which leads to well dispersed active components and stable crystal structure of catalysts.Meanwhile,the dopped Ce also results in a strong interaction between CuO and CeO₂ and then improve its mechanical strength and stabilize the active Cu species.The CeCu oxide catalyst can keep the original phase structure and surface morphology in recycle tests without significant change of surface element composition and valence state.Although the degradation effect of reused catalysts decreases to a certain extent in recycle tests,the amount of the leached active components decreases.The degradation of quinoline and bisphenol A can be well described by first-order reaction kinetics with the activation energies at 68.766 kJ/mol and 91.187 kJ/mol for quinoline and bisphenol A,respectively.This reflects that bisphenol A was more difficult to be degraded under the same conditions compared with quinoline,being consistent with the reaction results.The degradation of quinoline and bisphenol A follows the oxidative degradation mechanism of hydroxyl radicals,that is,the hydroxyl radicals attack the benzene ring in the molecule,thus forming a series of complex reactions.In the heterogeneous CWPO reaction system,the CeCu oxide catalysts can achieve the same catalytic oxidative degradation activity as that for Cu²⁺in homogeneous CWPO reaction system.The CeCu oxide catalysts can effectively catalyze the oxidative degradation of both quinoline and bisphenol A,which are two different types of organic substances,in a wide range of pH value.As another advantage for the CeCu catalysts,it was found that the CeCu catalysts will not result in precipitation in heterogeneous CWPO processes as the Cu²⁺does in homogeneous CWPO reactions.