Study On Thermocatalytic Decomposition Of Dimethyl Methylphosphonate Over Supported Transition Metal Oxide Catalysts

Chromium-free impregnated activated carbon adsorption is the traditional technology of protecting against toxic agents,which has problems such as narrow protection spectrum,failure after saturation and degradation after aging,and is not suitable for the growing demand for protecting against multiple nuclear,biological and chemical threats.The replacement technology has become a hot research topic.The thermocatalytic decomposition technology can decompose the poison molecules into non-toxic or low-toxic small molecular substances,showing a broad military application prospect.However,the heteroatoms contained in the poison molecules are liable to cause catalyst deactivation,and the development of efficient and stable catalysts is the key to this technology.Supported transition metal oxide catalysts have unique electronic structures and chemical properties,demonstrating the research value of thermocatalytic decomposition of toxic agents.The goal of this thesis is to obtain a superior catalyst formulation by studying the thermocatalytic decomposition performance of supported transition metal oxide catalysts for a sarin simulant,dimethyl methylphosphonate?DMMP?.The composition of product from thermocatalytic decomposition of DMMP was studied by means of various characterization methods.The reaction pathway of thermocatalytic decomposition of DMMP and the reasons for the decrease of catalyst activity were discussied.The supported single active component metal oxide catalysts were prepared by the incipient wetness method.The performance of thermocatalytic decomposition of DMMP over transition metal oxides?Ni,Fe,Cu,Mn,Co,Ce?supported on?-Al₂O₃ was studied.The performance of thermocatalytic decomposition over three kinds of common catalyst supports??-Al₂O₃,TiO₂,ZrO₂?loaded with the optimal active components was investigated.On the basis of the catalysts with the optimal composition,the loading amount of the active component was further optimized.The effects of reaction temperature and space velocity were studied.The experimental results showed that in the supported transition metal oxides,MO_x/?-Al₂O₃?M refers to Mn,Ni,Fe,Co,Cu and Ce?,the CuO component showed the best thermocatalytic decomposition performance.The protection time of 5%CuO/?-Al₂O₃ for DMMP reached 377 min at 400?.Among the supported CuO catalysts with?-Al₂O₃,TiO₂ and ZrO₂ as the supports,CuO/?-Al₂O₃showed the best thermocatalytic decomposition performance.The loading amount of CuO had a significant effect on the thermocatalytic decomposition performance of CuO/?-Al₂O₃ and 5%was the optimum ratio of CuO.Increasing the reaction temperature could prolong the protection time of 5%CuO/?-Al₂O₃ for DMMP,and reducing the reaction space velocity was beneficial to increase the amount of DMMP decomposed by 5%CuO/?-Al₂O₃.The thermocatalytic decomposition products of DMMP over 5%CuO/?-Al₂O₃ were studied by various analytical methods.The results of mass spectrometry and infrared gas analyzer showed that the gaseous products of thermocatalytic decomposition of DMMP over 5%CuO/?-Al₂O₃ included methane,methanol,hydrogen and carbon dioxide.No carbon monoxide or organic phosphorous products were detected.The results of X-ray photoelectron spectroscopy,infrared spectroscopy,ion chromatography and ICP-OES showed that the surface and the bulk phase of the penetrated 5%CuO/?-Al₂O₃ contained much phosphorus.The phosphorous species on the catalyst surface included phosphoric acid and methylphosphonic acid.The deposition of surface phosphorous species and the formation of metal phosphate destroyed the pore structure and crystal structure of the catalyst,which were main reasons for the decrease of the thermocatalytic decomposition activity of 5%CuO/?-Al₂O₃.In order to further improve the performance of thermocatalytic decomposition of DMMP over supported CuO catalysts,the supported double active component metal oxide catalysts,CuO-MO_x/?-Al₂O₃?M refers to Fe,Mn and Ce?,were prepared by the co-impregnation method.The effects of the second active component on the performance of thermocatalytic decomposition of DMMP over CuO-MO_x/?-Al₂O₃ were studied.The optimal loading amount of the second active component was also studied.The mechanism of the second active component affecting the catalytic performance of the catalyst was discussed.The experimental results showed that the supported double active component catalyst,CuO-MO_x/?-Al₂O₃?M refers to Fe,Mn and Ce?,exhibited better thermocatalytic decomposition performance than 5%CuO/?-Al₂O₃,and the performance of the catalyst with CeO₂ used as the second active component was optimal.When the loading amount of CuO was 5%,with increasing loading amount of CeO₂?1%,5%,10%?,the protection time of the supported copper and cerium catalyst increased firstly and then decreased.The optimum loading amount of CeO₂ was 5%,and the protection time of the catalyst for DMMP reached 237 min at 350?.The results of XRD,XPS and H₂-TPR showed that the Cu and Ce components in the catalyst had strong interaction,and the mode of the interaction may include the doping of the CeO₂ lattice by the Cu component.The interaction promoted the formation of surface-adsorbed oxygen,which was beneficial to thermocatalytic decomposition of DMMP.