Preparation And Performance Of Composite Metal Oxide Catalysts And Their Catalytic Oxidationof Toluene And Formaldehyde

Nowadays,with the improvement of industrialization and people’s lives,which made people realize that the importance of protecting the environment.Volatile organic compounds（VOCs）are one of the common gas pollutants in the atmosphere.At present,one of the widely used methods to control VOCs emissions is catalytic oxidation technology,and transition metal composite oxides are commonly used catalysts for the removal of volatile organic pollutants by catalytic oxidation due to their better oxidation-reduction capabilities.However,the catalyst structure synthesized by the traditional preparation method is relatively poor,and it is difficult to achieve the expected catalytic efficiency.It is of great significance to improve the preparation method of catalyst,adjust the composition of active components of catalyst and improve the effect of VOCs removal.In this paper,toluene and formaldehyde were selected as probe reactants to prepare efficient Ni_xCe_yO₂,Co_xZr_yO₂,Co_xCe_yO₂composite oxide catalysts.The optimal ratio of active metal in the three metal composite oxides above was studied,and the relationship between the physical and chemical properties of the catalysts and their catalytic performance was explored.1.The spherical and rod-shaped ceria t were prepared by the citric acid sol-gel method to support Ni_xCe_yO₂metal composite oxides with different doping amounts of Ni O.The catalytic oxidation performance of toluene was investigated.Ni₁-S-Ce O₂was due to its large surface area(79 m²·g^-1),moderate grain size,porous structure inside,more oxygen species adsorbed on the surface respectively.Thus it has the best catalytic activity,the conversion temperature of 90%toluene oxidation is 107℃.2.Co_xZr_yO₂metal composite oxides with different doping amounts of Co were prepared by hydrothermal method,precipitation method,thermal decomposition method and impregnation method.The catalytic oxidation performance of toluene and formaldehyde was investigated.The catalyst of Co_xZr_1-xO₂-H（1:1）showed the best catalytic activity due to its specific surface area of 102 m²·g^-1and better synergism between cobalt and zirconium.At 225℃ and 115℃,toluene and formaldehyde can be completely oxidized and the apparent activation energy is as low as 65.2kJ·mo^l-1and 53.6kJ·mol^-1,respectively.3.Co_xCe_yO₂composite oxide was prepared by vacuum assisted impregnation method and ordinary impregnation method using KIT-6 as template.The catalytic oxidation performance of toluene was investigated.Co₃O₄-Ce O₂composite oxide prepared by vacuum assisted impregnation method has better catalytic oxidation performance for toluene due to significantly increased specific surface area and well-developed ordered mesoporous structure.The reaction temperature is 261℃ when toluene is completely transformed.