Preparation Of Hydrotalcite-like Catalyst And Its Catalytic Oxidation Performance For Toluene Removal

Volatile organic pollutants（VOCs）,as a kind of important air pollutants,mainly come from petroleum refining,organic chemical industry,medicine,automobile exhaust,machinery manufacturing and other industries.VOCs can easily cause serious environmental problems such as photochemical pollution,ozone layer destruction,haze,etc.,and can harm human health through the"three effects".There are many types and sources of VOCs,and it is difficult to control them.Among many VOCs removal technologies,catalytic oxidation technology has significant advantages such as low energy consumption,simple operation,high degree of VOCs mineralization,and no secondary pollution,which has attracted extensive attention of researchers.The key to catalytic oxidation technology is the development of efficient catalysts.Among many types of catalysts,The hydrotalcite-derived oxide catalyst obtained by using hydrotalcite as a precursor has the advantages of uniform dispersion of active elements,structural and compositional modification,etc.,so that the prepared catalyst can fully exert the synergistic effect between elements,has certain development prospects.In this paper,the typical VOCs toluene was used as the target pollutant to study the VOCs catalytic oxidation performance of hydrotalcite-derived oxide（LDO）catalysts,and the catalyst reaction performance was optimized by adjusting the element composition of hydrotalcite and improving the catalyst preparation process.The main research results of this paper are as follows:（1）Different kinds of LDO catalysts such as Mg₃Al₁,Mg₃Fe₁,Cu₃Al₁,Co₃Al₁were synthesized,and the effects of catalyst element composition,active species loading method and catalyst calcination temperature on the physicochemical properties and catalytic reaction performance of the catalyst were studied.The study found that the Mg₃Al₁-Ce10%（A-500）catalyst prepared by adsorption loading method with Mg₃Al₁ hydrotalcite derivative（Mg₃Al₁-LDO）as the carrier had the best catalytic oxidation performance of toluene,in which the T50 decreased to 280℃,and the T90 decreased to 312°C.And the physicochemical properties of the catalyst were studied by characterization method,and it was found that the active species in the catalyst obtained by this preparation method can be uniformly supported on the surface of Mg₃Al₁-LDO,and CeO₂ has good oxygen storage and transfer performance,so that CeO₂ can give full play to the performance its performance.Finally,the mechanism of different oxygen species in the catalytic oxidation of toluene was explored based on the Mars-van Krevelen mechanism,and it was found that abundant surface oxygen species was the key to the excellent performance of the catalyst.（2）The effect of partial substitution of hydrotalcite precursor A site on the catalytic oxidation performance of Ce/LDO catalyst for toluene was studied.The study found that the use of Co element to replace part of the Mg element in the Mg₃Al₁ hydrotalcite precursor can significantly improve the low temperature activity of the Mg₃Al₁-Ce10%（A-500）catalyst,the Mg/Co molar ratio is 2.25/0.75,and the Celoading is 10 At wt.%,the T90 temperature of toluene oxidation decreased to283℃.The Co₃O₄ and CeO₂species in the catalyst produce strong interactions,and the redox process between Co³⁺/Co²⁺and Ce⁴⁺/Ce³⁺promotes the generation of oxygen vacancies and enhances the lattice oxygen mobility,thereby promoting the adsorption and oxidation of toluene.（3）The catalytic oxidation mechanism of toluene on typical catalysts was investigated by in situ infrared spectroscopy.The study found that the reaction process of toluene catalytic oxidation is as follows:gas-phase toluene molecules are adsorbed on the surface of the catalyst,then attacked by active oxygen,and initially activated to benzoic acid,benzyl alcohol,and benzoic acid,and then the benzene ring is opened to produce maleate.,aliphatic carboxylates and small molecular aldehydes,and then the ring-opening product reacts to generate carbonate substances,which are mineralized into carbon dioxide and water.Among them,the ring-opening reaction of the benzene ring is the key step in the oxidation of toluene.