Investigation On CO Oxidation Properties Of 3DOM Co-Based Catalysts And Their Application In Cigarette Filters

Carbon monoxide（CO）is one of the seven most harmful substances in mainstream smoke of cigarettes.How to effectively reduce the carbon monoxide level in cigarette smoke without affecting the smoking quality has become a great challenge faced by the tobacco industry.According to the source of CO in mainstream smoke,it can be removed from three directions: tobacco raw materials,combustion process and cigarette smoke post-treatment.To some extent,controlling the raw materials（Optimized cultivation method,Reduced tobacco use）and improving the combustion process（Improve the permeability of cigarette paper,molding paper and mounting paper,Change the size of cigarette）can lower CO and other harmful components.In the meanwhile,it can also bring about the issues which affects suction quality,such as insufficient suction and aroma dissipation.However,the cigarette smoke post-treatment uses high-performance catalyst to reduce the amount of CO and other harmful components in the smoke,but it can maximizing maintain the smoke quality of cigarettes to the maximum extent.The core of this technology is the development of catalysts with high catalytic activity at low temperatures.Therefore,based on contact characteristic of CO catalytic reaction（gas-solid-gas）,a transition metal oxide catalyst with a three-dimensional ordered macropore structure（3DOM structure）was designed from intrinsic activity and morphological contact.The 3D-Co_xCe₁O_y and 3Dx%AgCo₁₆Ce₁ catalysts were prepared by doping and double doping,and various characterization methods were analyzed their physical and chemical characteristics.In addition,the mechanism of CO catalytic reaction was investigated basis on DFT simulation.The followings are the main research contents and conclusions of this paper:Firstly,a series of 3D-Co_xCe₁O_y catalysts with different doping amounts were prepared by PMMA template impregnation method.Phase characterization,chemisorption characterization,CO catalytic activity and DFT theoretical calculation showed that:（1）In terms of intrinsic activity: Ce doping increased the concentration of oxygen vacancy in 3D-Co_xCe₁O_y,and increased the content of Co³⁺ by regulating the conversion between Ce⁴⁺+Co²⁺→Co³⁺+Ce³⁺,thus improving the catalyst activity;（2）In terms of morphology contact: The 3DOM structure not only facilitates to the mass transfer and diffusion of CO gas,but also increase the contact area between CO and the active site;（3）Under the synergic promotion of intrinsic activity and morphology contact,3D-Co_xCe₁O_y showed the best CO catalytic performance（T50=124.8℃）and the lowest activation energy（Ea=98.85 k J/mol）.In addition,the cyclic stability and 24 h continuous reaction tests showed that the catalyst had strong thermal stability.Secondly,based on the morphological contact advantage of 3D-Co_xCe₁O_y catalyst,in order to further improve the activity of the catalyst,the precious metal element Ag was introduced by doping,and the double-doped 3D-x%Ag Co16Ce1 catalyst was prepared.A series of characterization studies showed that:（1）3D-x%Ag Co16Ce1 catalyst could further improve the CO catalytic activity of catalyst(3D-Co₁₆Ce₁O_y)on the basis of single Ce component doping,and basically meet the range of cigarette filter temperature;（2）Through XPS and DFT theoretical calculation,the internal mechanism of catalyst activity enhancement of 3D-x%Ag Co16Ce1 was proposed: This catalyst was based on the 3DOM morphological structure and single Ce component doping(Ce⁴⁺+Co²⁺→Co³⁺+Ce³⁺),and the percentage of Co³⁺ ions and surface active oxygen species in the catalyst was further enhanced by the conversion between Co²⁺+Ag+→Ag0+Co³⁺;（3）The optimal sample 3D-5Ag%Co16Ce1 showed the best CO（T50=53.3℃）catalytic activity and the lowest activation energy（Ea=48.79 k J/mol）,and showed good thermal stability in the cyclic stability test.Finally,a composite filter（Catalyst acetate fiber filter）was prepared by a combination of impregnation and freeze-drying.The removal effect of the composite filter on CO and other harmful components was investigated by smoking machine and GC-MS analysis.The results are as follows:（1）The optimal catalyst dosage for the composite filter is 20mg/piece,too much catalyst will cause the destruction of the acetic acid fiber structure of the filter,and then affect the number of suction ports and suction feeling;（2）The results showed that the removal rates of CO and total particulate matter in mainstream flue gas by composite filter-B were above 25% at a catalyst addition of 20 mg,which exhibited good mainstream smoke harm reduction effects.