Reaction Mechanism And Optimization Of The Ceria-Based Catalysts In The Catalytic Destruction Of Chlorobenzene

Developing a catalytic system with good chlorine resistance and exploring suitable reaction condition are the keys to deal with chlorinated volatile organic compounds?Cl-VOCs?by catalytic combustion technology.In this paper,based on the ceria-based catalyst with advanced redox property,the reaction mechanism of catalytic purification of chlorobenzene with the optimized catalyst was explored,and the importance of the coordination of adsorption and oxidation sites,as well as the effect of efficient adsorption and activation of water vapor on catalyst dechlorination and product selectivity was investigated.On this basis,the catalyst of nano-rod Ce O₂ supported by phosphate groups was developed,which realizing a highly efficient coordination of hydrolysis dechlorination and deep oxidation by oxygen vacancies,and the efficiently stable purification of Cl-VOCs was realized ultimately.This provided experimental and theoretical basis for the optimal design of ceria-based catalyst and its application in Cl-VOCs catalytic purification.In this paper,chlorobenzene was selected as the representative Cl-VOCs and the rod-shaped nano Ce O₂ was used as the matrix material.By loading acid molecular sieve HZSM-5,the adsorption and oxidation sites of chlorobenzene on the catalyst surface were separated.It was found that the isolation adsorption of chlorobenzene could protect the oxygen vacancy,thus facilitate the stability of the reaction,and inhibit the chlorine poisoning of the catalyst.However,the increase of mass transfer distance of reactants decreased the performance for deep oxidation of chlorobenzene and promoted the formation of high toxic polychlorinated by-products.This paper subsequently studied the way to effectively remove the chlorine on the catalyst surface to inhibit the formation of high toxic polychlorinated by-products.Through the catalytic oxidation test of chlorobenzene with Au/Ce catalysts in wet condition,it was found that Au modification could significantly improve the conversion rate,selectivity and stability of catalytic purification of chlorobenzene,which was related to the advanced water adsorption and activation performance of Au.In addition,it was clarified that the loading of Au must be kept moderate to balance the relationship between the deep oxidation ability and the adsorption and activation ability of water vapor.Based on the above researches,the inorganic phosphoric acid was then used to modify Ce O₂ to introduce phosphate groups,which could purify chlorobenzene by hydrolysis reaction.The experimental results showed that the phosphate modification could greatly enhance the adsorption and activation of water,and promote the desorption of chlorine,thus significantly inhibit the generation of polychlorinated by-products.Further physicochemical characterizations and DFT calculations revealed that the phosphate groups mainly existed in the form of amorphous orthophosphates,and phosphate modification could effectively enhance the acidity and redox performance,as well as promote the adsorption and deep oxidation of chlorobenzene.The hydrolysis of chlorobenzene on the surface of HP-Ce O₂ tended to follow the E-R reaction model.In the reaction process,the selective adsorption of water on the phosphate groups would transform the 2-OH phosphate into 3-OH structure,which was very conducive to the formation and desorption of HCl,thus stabilizing the catalytic purification reaction of chlorobenzene and inhibiting the generation of polychlorinated by-products.