Synthesis Of Co₃O₄ Based Catalytic Materials And Application For Catalytic Elimination Of VOCs

As an important precursor of fine particulate matter（PM2.5）and ozone（O₃）,volatile organic compounds（VOCs）is a very serious air pollutant,which not only causes ozone and photochemical smog and thus causes environmental pollution,but also seriously endangers people’s life and health.Therefore,the VOCs elimination is very important for haze control.Due to its low cost and no secondary pollution,catalytic oxidation technology has been widely used to eliminate VOCs.The key to catalytic oxidation is the catalyst,whose catalytic performance determines the removal rate of VOCs.As a typical transition metal oxide,Co₃O₄ has a high catalytic activity on VOCs catalytic oxidation reaction as a carrier or active component,and is a hot spot in VOCs catalytic oxidation research.Starting from this point,this paper mainly carried out the following work:study the influence of catalyst particle size on the dispersion of Co₃O₄ catalyst active components supported by noble metals;the controlled synthesis of MOFs-derived Co₃O₄ catalyst particle size was studied.The morphology control condition of metal oxide catalyst was studied to obtain Co₃O₄based catalyst with high activity.Base on this,SEM,TEM,XRD,BET,H₂-TPR,XPS,Raman,TG,FTIR and other characterization techniques were used to study the factors affecting the activity of Co₃O₄ based catalytic materials.The research results are as follows:Porous Co₃O₄ nanocatalyst with size-controlled was prepared by solvent thermal method.On this basis,Pd/Co₃O₄ catalysts were prepared by impregnation method for toluene catalytic oxidation.The results showed that ethanol as the solvent of the preparation of catalyst（Pd/Co₃O₄-E）has good toluene catalytic properties,When the weight hourly space velocity was 21000 mL g^-11 h^-1,the total conversion temperature(T₁₀₀)is 200℃.Meanwhile,a series of instruments were used to characterize the factors affecting the performance of the catalyst.SEM and TEM results showed that Pd/Co₃O₄ catalyst synthesized with different solvents had different particle sizes and Pd/Co₃O₄-E had the largest particle size,about 13.6 nm.Through a series of characterization analysis,it was believed that the performance of Pd/Co₃O₄ catalyst is related to the specific surface area of the catalyst,the adsorbed oxygen on the surface,the dispersion of Pd nanoparticles,and the synergistic effect of Pd nanoparticles and Co₃O₄.The precursors of ZIF-67 with different sizes were synthesized by varying reflux solvent and reaction temperature.A series of hollow Co₃O₄ polyhedron with different sizes were synthesized by pyrolysis of ZIF-67.Meanwhile,The size effect of the hollow Co₃O₄ polyhedron on the catalytic oxidation of toluene was studied.According to the results of SEM and TEM,the sample still retained the nanosize and shape of the MOF precursor.Co₃O₄-400（size was 400 nm）catalysts shows excellent catalytic performance,T₁₀₀00 was 280℃.Through a series of characterizations,the particle size of the hollow Co₃O₄ polyhedron could significantly alter the surface atomic ratio of Co³⁺/(Co³⁺+Co²⁺)and surface adsorbed oxygen.The smaller the particle size of catalyst,the higher the ratio of Co³⁺/(Co³⁺+Co²⁺)and the higher surface adsorbed oxygen concentration.With the increase of surface atomic ratio of Co³⁺/(Co³⁺+Co²⁺),the catalytic performance of hollow Co₃O₄ polyhedron is obviously improved.At the same time,Co₃O₄-400 catalyst show the oxidation of toluene with good stability because it could maintain its catalytic performance for more than 30 h under the 250℃.Three different structures of Mn_xCo_3-xO₄ were successfully synthesized by optimizing the heating decomposition conditions of Mn@Co-ZIFs precursors to form three types Mn_xCo_3-xO₄ catalysts with different morphology,including the hollow Mn_xCo_3-x-x O₄ polyhedron(HW-Mn_xCo_3-xO₄),Box-In-Ball Mn_xCo_3-x-x O₄ polyhedron(BIB-Mn_xCo_3-xO₄)and nanoparticle Mn_xCo_3-xO₄ polyhedron(NP-Mn_xCo_3-x-x O₄).The structure effect of Mn_xCo_3-xO₄ polyhedron on the catalytic oxidation of toluene was systematically investigated.It could be noted that the HW-Mn_xCo_3-xO₄ sample exhibited superior catalytic performance,and the complete conversion temperature of toluene(T₁₀₀)was 195°C.Furthermore,HW-Mn_xCo_3-xO₄ sample exhibited excellent stability for toluene oxidation reaction.Through a series of characterizations,it was concluded that the morphology and structures of Mn_xCo_3-x-x O₄ catalysts could evidently alter the surface atomic ratio of Co²⁺/(Co³⁺+Co²⁺),BET surface area,the number of surface adsorbed oxygen,the interaction between Mn and Co₃O₄ and so on.Especially,we discovered that the catalytic activity of Mn_xCo_3-xO₄ polyhedron was obviously improved with the increase of surface atomic ratio of Co²⁺/(Co³⁺+Co²⁺).In addition,large BET surface area,lots of surface adsorbed oxygen,strong interaction between Mn and Co₃O₄ would speed up the catalytic oxidation of toluene.