Thermocatalytic Decomposition Of Dimethyl Methylphosphonate On MO_x/CeO₂ Nano-catalysts

For the removal of toxic agents in the air,traditional adsorption technology is still used.However,it has adsorption saturation and cannot destroy the toxic molecular structure and requires secondary treatment.At present,industrial thermal catalytic decomposition technology is a very effective gas pollutant purification technology,which is widely used in the purification of various organic volatile pollutants and small molecule inorganic pollutants.Thermal catalytic decomposition technology has potential military applications.Therefore,it is significant to design and prepare catalysts suitable for thermocatalytic removal of CWAs as well as the mechanism of thermocatalytic decomposition of CWAs on the catalysts and the mechanism of catalyst poisoning.In this work,CeO₂ nanomaterials with different morphologies and MO_x/CeO₂（M:Cu,Mn,Fe）nanocatalysts were prepared,and the physicochemical properties of various catalysts were characterized,and the optimal catalyst combinations were obtained through the study of the thermal catalytic decomposition of dimethyl methylphosphonate（DMMP）by CeO₂ nanomaterials and MO_x/CeO₂ catalysts.The mechanism of thermal catalytic DMMP decomposition by different catalysts and the mechanism of catalyst poisoning were proposed through the analysis of DMMP decomposition products and the evolution of catalyst surface species during the decomposition reaction.The main studies are as follows:The CeO₂ catalysts were synthesized by hydrothermal method.Three morphologies of CeO₂ nanocatalysts,irregular nanoparticles,nanorods and nanocubes,were prepared by adjusting the hydrothermal reaction temperature and Na OH concentration.The thermal catalytic decomposition DMMP performance of CeO₂ catalysts for was investigated by a self-built catalyst evaluation device.The oxidation activity,Ce elemental valence and oxygen vacancy concentration of CeO₂ catalysts were investigated using various characterization techniques.The best nanoparticle,nanorod and nanocubic CeO₂ catalysts for the thermal catalytic decomposition DMMP performance were selected,and the products of thermocatalytic DMMP decomposition,the reaction mechanism of thermocatalytic DMMP decomposition and catalyst poisoning mechanism were studied on three morphologies of CeO₂ nanocatalysts.The experimental results showed that Ce³⁺ions were presented on the surface of all three morphologies of CeO₂ catalysts,and the stronger oxidation activity and more oxygen vacancies of CeO₂ nanorods led to the best performance of CeO₂ nanorods for thermocatalytic DMMP decomposition.Based on the analysis of reaction products and the evolution of catalyst surface species during the reaction,the reaction mechanism of thermocatalytic DMMP decomposition on CeO₂ nanomaterials and the catalyst poisoning mechanism were proposed.It was found that surface defective oxygen plays a crucial role in the thermocatalytic DMMP decomposition.The main reaction paths of the catalytic decomposition of DMMP were similar for the three morphologies of CeO₂,but the reaction paths of the three forms of CeO₂ are different in the side reactions involving methanol.The accumulation of phosphate,carbonate and formate on the catalyst surface is the main factor for catalyst deactivation.The FeO_x/CeO₂ catalysts with different Fe/Ce ratios（10%,20%,50%,80%）were prepared by compounding CeO₂ nanorods with FeO_x using a modified secondary alkaline hydrothermal method.The physicochemical properties of FeO_x/CeO₂ catalysts were investigated using various characterization methods.The performance of thermocatalytic DMMP decomposition on FeO_x/CeO₂ catalysts was investigated by a self-built catalyst evaluation device.The FeO_x of FeO_x/CeO₂ catalysts was mainly Fe₂O₃.The catalyst morphology and elemental distribution were characterized by TEM and EDX,it was found that Fe atoms uniformly distributed on the surface of CeO₂ nanorods and Ce atoms uniformly distributed on the surface of FeO_x nanoparticles in FeO_x/CeO₂ catalyst.Electron transfer between Fe and Ce ions was found by analyzing the valence states of the surface metal elements.The interaction between FeO_x and CeO₂ led to the enhancement of the performance of thermocatalytic DMMP decomposition on FeO_x/CeO₂ catalysts.Combined decomposition products with the change of catalyst surface species during the reaction,the mechanism of thermal catalytic DMMP decomposition on CeO₂,FeO_x/CeO₂ and FeO_x and the mechanism of catalyst poisoning were proposed.It was found that the catalytic decomposition pathway of DMMP on FeO_x/CeO₂ and FeO_x was basically the same as that on CeO₂,but there was no formate on FeO_x and FeO_x/CeO₂.The accumulation of phosphorus and carbon products on the catalyst surface leads to toxic inactivation of the catalysts.The CuO/CeO₂ catalysts with different Cu/Ce ratios（10%,20%,50%,80%）were prepared by compounding CeO₂ nanorods with CuO.Cu atoms are uniformly distributed on the surface of CeO₂ nanorods in CuO/CeO₂ catalysts.The analysis of the oxidation activity and metal element valence state of CuO/CeO₂ catalysts revealed that the oxidation activity of CuO/CeO₂ catalysts was significantly enhanced and there was reversible electron transfer between Cu and Ce ions.The strong interaction between CuO and CeO₂ led to the significantly enhanced the performance of thermocatalytic DMMP decomposition on CuO/CeO₂ catalysts.It was found that the the main catalytic decomposition pathways of DMMP on CuO and CuO/CeO₂ were basically the same as on CeO₂,while only carbonate by-products were formed on the surface of CuO and CuO/CeO₂ catalysts.The accumulation of phosphorus and carbon products on the catalyst surface leads to catalyst poisoning and deactivation.The MnO_x/CeO₂ catalysts with different Mn/Ce ratios（10%,20%,50%,80%）were prepared by compounding CeO₂ nanorods with MnO_x.The MnO_x of MnO_x/CeO₂ catalysts were consisted of Mn₃O₄ and MnO₂,and it was found that there was obvious dissolution of CeO₂ nanorods during the secondary alkaline hydrothermal reaction,and Mn atoms were uniformly distributed in CeO₂ nanorods.By analyzing the oxidation activity and metal element valence of the catalysts,the oxidation activity of the MnO_x/CeO₂ catalyst was enhanced and reversible electron transfer between Mn and Ce.The strong interaction between MnO_x and CeO₂ resulted in the performance thermal catalytic DMMP decompositionthe on MnO_x/CeO₂ catalysts was significantly enhanced.The mechanism of thermocatalytic decomposition of DMMP on MnO_x/CeO₂ and MnO_x and the mechanism of catalyst poisoning were proposed by studying the reaction products and the evolution of catalyst surface species during the reaction.The P-CH₃ bond breakage may cause the MnO_x/CeO₂ catalyst to have better resistance to poisoning than the CuO/CeO₂ catalyst.The accumulation of phosphorus product and carbon product on the catalyst surface leads to catalyst poisoning deactivation.We have systematically investigated the thermocatalytic decomposition of DMMP on CeO₂nanomaterials and MO_x/CeO₂ catalysts to provide a reference to design of high-performance catalysts for efficient degradation of chemical toxicants in the future.