Construction Of ?@?-MnO₂ Catalyst And Its Performance For Toluene Catalytic Oxidation

Catalytic oxidation technology is currently widely used in the treatment of volatile organic pollutants,and its core is the construction of catalysts.Transition metal oxide catalysts have always been a research hotspot because of their low price,enviromentally friendliness and good stability,however,the improvement of its low-temperature catalytic oxidation performance is a difficult point.The construction of layered nanostructures with interfaces can effectively improve the function of the catalyst.The transition metal manganese dioxide possesses polymorphisms??-??-??-??-etc.?,as well as the ability to store oxygen and release oxygen well,and thus can switch between different valence states for rapid redox reactions.Therefore,in order to remove volatile organic pollutants more effectively,a one-step hydrothermal method using potassium permanganate?KMnO4?and oxalic acid?H₂C₂O₄·2H₂O?is used to optimize the synthesis conditions for the preparation of pure-phase?-MnO₂ and?-MnO₂ and mixed phase MnO₂ catalyst.The influence of the phase structure of MnO₂ on the catalytic activity of toluene and the interaction of heterogeneous catalysts are discussed.The specific research contents and results are as follows:?1?Effect of preparation conditions of MnO₂ catalyst on its crystal structure and catalytic performance.Through the hydrothermal synthesis conditions of KMnO₄ and H₂C₂O₄·2H₂O,it is found that H₂C₂O₄·2H₂O concentration and hydrothermal temperature affect the MnO₂crystal phase.When the ratio of KMnO₄ and H₂C₂O₄·2H₂O is 1:1.8,the mixed-phase MnO₂??@?-MnO₂?can be prepared in one step hydrothermally by changing the hydrothermal temperature.?2?The influence of the structure and interaction of?@?-MnO₂ catalysts on the catalytic performance of toluene,the experimental results show that the catalytic activity of toluene oxidation is in the following order:?@?-MnO₂>?-MnO₂>?-MnO₂.Compared with the pure phase catalyst,?@?-MnO₂ catalyst has active interface structures and a large concentration of oxygen vacancies.The interfacial structure makes the catalysts have a strong synergistic effect.Oxygen vacancies are conducive to the enhancement of the activity of the adjacent lattice oxygen and the adsorption and activation of the reactants.Thus,?@?-MnO₂catalysts have sufficient active oxygen species,excellent low temperature reducibility,and strong activation and reactivity to the reactants.In-situ IR results show that pure phase catalysts can only oxidize toluene to benzaldehyde intermediates at room temperature,whereas?@?-MnO2 with rich reactive oxygen species can oxidize toluene to the active intermediate carboxylate salt at room temperature.So?@?-MnO₂ show good performance of low temperature oxidation catalytic oxidation of toluene,and the toluene conversion temperature of 205-220^oC.?3?The proportions of?-MnO2 and?-MnO2 in the?@?-MnO2 catalyst directly affect the structure of the catalyst and thus affect the catalytic performance.In the Mb catalyst,when the ratio of?-MnO₂ and?-MnO₂ is 1:1,the catalyst has the largest amount of interfacial structure and oxygen vacancy concentration,and there is a strong synergistic effect,which is favorable for the catalyst to exhibit the best catalytic activity,and the complete conversion temperature is around 205^oC.