Study On Manganese-based Catalysts For Combustion Of 1,2-dichloroethane

With rapid urbanization and industrialization,human activities release more and more chlorinated volatile organic compounds（CVOCs）,leading to rapid increases in PM2.5 and ozone concentrations,photochemical smog,and frequent hazy weather.Among them,1,2-dichloroethane（1,2-DCE）,a typical representative substance of CVOCs,is emitted from a wide range of sources,from industrial processes such as pharmaceutical manufacturing and coating and printing.Catalytic combustion has attracted extensive research because of its advantages of high efficiency and low energy consumption.In this study,different crystal phases of Mn O₂ and zeolite loaded Mn catalysts with different topologies were prepared for the catalytic combustion of 1,2-DCE,and a series of characterization techniques were used to characterize the differences between various catalysts and reveal the conformational relationships between the whole reaction process.1.The preparation of four kinds ofα-,β-,γ-,andδ-type Mn O₂ with distinct crystal phases and tunnel structures were achieved and applied for1,2-DCE catalytic combustion.The redox ability and acidity of Mn O₂ as well as the corresponding reaction mechanism were studied by means of various surface-sensitive techniques,including TPR,TPD,OIE,XPS,in situ DRIFTS together with DFT calculation.The catalytic activities in 1,2-DCE combustion illustrated thatγ-Mn O₂ displayed the most superior activity with the maximum HCl yield of 95%and CO₂ yield of 92%,due to it is easy to form abundant oxygen vacancies on its surface,which are enriched and decomposed into a large number of reactive oxygen species,and these oxygen species have a strong migration ability and can easily react with the adsorbed reactants to produce HCl.However,the large amount of Mn⁴⁺inβ-andδ-Mn O₂ formed strong Mn-Cl bonds with dissociated Cl and the oxygen atoms bonded to Mn⁴⁺were not easily detached to participate in the reaction,hindering their HCl elimination process,even through the Cl substitution process leading to with a series of polychlorine byproducts including 1,1,2-C₂H₃Cl₃ and CCl₄,and generating chlorine deposition.Therefore,the mechanism of 1,2-DCE combustion is proposed,and active chlorine substitution and dehydrochlorination reactions are the main means of generating polychlorinated products,and excellent redox properties can accelerate further oxidation reactions of chlorine-containing by-products to be converted.2.The catalytic combustion study of 1,2-DCE was carried out using Mn-based zeolite catalysts with different topologies,and the three-dimensional 10-membered ring（10-MR）structure of the zeolite catalyst（Mn/ZSM-5）was found to have better activity as well as resistance to chlorine poisoning and excellent CO₂ yield（83%）and HCl yield（100%）by various characterization techniques such as TPR,TPD,XPS and nitrogen adsorption and desorption.The medium pore 10-membered ring and small pore 8-MR pore structures are less catalytically active,while the large pore 12-MR pore structure increases the yield of chlorine-containing by-products.The highly dispersed Mn³⁺species were also found to be the main active site,adsorbed oxygen and small amounts of lattice oxygen contribute to the reaction and the three-dimensional 10-MR pore structure and abundant cross-pore channels enhanced the catalytic activity of the whole reaction,and the different topologies of Mn-based zeolite enhanced the acidity compared with different crystal phases of Mn O₂,resulting in a decrease in the species and yield of chlorine-containing byproducts.In summary,it is more evident that the improvement of strong acidity and redox properties can enhance the anti-poisoning ability of the catalyst.And a simple reaction pathway was inferred from in-situ DRIFTS as well as GC-MS:1,2-DCE→Vinyl chloride（VC）→dichloroethylene→alcohols→aldehydes→acetate species→carbonate species→CO,CO₂ and H₂O.