Study On The Catalytic Performance Of La(Mn) Modified Co₃O₄ Catalysts For The Oxidation Of Toluene

Volatile organic compounds(VOCs)have been considered as one of the main environmental pollutants which are seriously harmful to the environment and human health.Catalytic oxidation technology is considered as the most promising technology for VOCs removing because of its low energy consumption and no secondary pollution.In recent years,Co₃O₄ has been widely studied among transition metal oxides due to its spinel structure,low cost and high catalytic activity.In this thesis,for the disadvantages of Co₃O₄ catalyst,the catalysts were modified by morphology and elements.Catalytic oxidation of toluene was used as a model reaction to learn the relationship structure and performance which were analyzed by XRD,SEM,TEM,XPS,N₂ adsorption-desorption,H₂-TPR,O₂-TPD and in-situ DRIFTS.Co₃O₄ catalysts with different morphologies were synthesized by solvothermal method.The result shows that the catalysts synthesized by different cobalt source,surfactant and solvent exhibit different morphologies(spherical Co₃O₄(S)accumulated by nanocubes,bow shaped Co₃O₄(F)stacked by sheets and block Co₃O₄(B)deposited by nanoparticles).Co₃O₄(S)and Co₃O₄(F)catalysts have higher surface Co³⁺and surface lattice oxygen content,and exhibit better catalytic ability.T₅₀(the temperature of 50%toluene conversion)of Co₃O₄(S)and Co₃O₄(F)and Co₃O₄(B)are 234,242 and246 ?,respectively.T₉₀(the temperature of 90%toluene conversion)are 246,250 and263 ?,respectively.Obviously,the activities at low temperature needs to improve.In order to improve the activity at low temperature of Co₃O₄ catalyst,a series of La_aCo_1-aO_x catalysts were synthesized by solvothermal method.The physicochemical properties of catalysts were analyzed by a sort of characterizations.T₅₀ of La_0.01Co_0.99O_x,La_0.02Co_0.98O_x,La_0.03Co_0.97O_x and La_0.04Co_0.96O_x catalysts are 224,224,213 and 220 ?,respectively.The results exhibit that the doping of La can improve the low temperature activity of the catalysts.Among them,La_0.03Co_0.97O_x shows the best catalytic activity.The doping of La increases the specific surface area,Co³⁺and surface adsorbed oxygen species content,which are conducive to the catalytic oxidation of toluene.At 225 ?,the toluene conversion rate of La_0.03Co_0.97O_x catalyst could maintain 90%within 10hours,and then gradually decreased to 78%.The conversion of toluene(90%)tested at225 ? is unchanged over La_0.03Co_0.97O_x in 10 h,and then down to 78%.In order to promote the activity at low temperature and activity stability of Co₃O₄catalyst simultaneously,a series of Mn_aCo_1-aO_x spinel catalysts is obtained by introducing Mn with various valance into Co₃O₄ catalyst.A series of characterization results show that the doping of Mn influences the morphology of the catalyst,increases the specific surface area,enhances the REDOX performance of the catalyst,changes the surface element composition of the catalyst,and greatly improves the low temperature activity of the catalyst.Among them,Mn_0.4Co_0.6O_x catalyst exhibits the best activity,T₅₀and T₉₀ are 206 and 215 ?,respectively.The conversion of toluene(90%)tested at 215? is unchanged over Mn_0.4Co_0.6O_x under WHSV of 40,000 m L/(g·h)in 24 h.In addition,in situ DRIFTS shows that the oxidation process of toluene follows Mv K mechanism,and surface lattice oxygen plays a major role.