Preparation Of Co-based Catalysts And Their Catalytic Performance For Volatile Organic Compounds Oxidation

Volatile organic compounds（VOCs）,have great threats to human and environment,are one of the air pollutants.Catalytic oxidation at low temperature has been considered as one of the most efficient treatment technologies.In this dissertation,according to the characteristics of structural controllability,controllable shape,high dispersion of active composition and high temperature resistance of hydrotalcite-like compounds,we have designed a series of Co-based oxides with specific structure and investigated their catalytic performance,stability and reaction mechanism for VOCs oxidation.Subsequently,CoAlO oxides with different morphologies have been designed and modified by KMnO₄.Besides,considering the nickel foam of three-dimensional structure as the framework,we have prepared a series of monolithic catalysts with Ni foam.The morphology transition,catalytic performance and reaction mechanism of monolithic catalysts with Ni foam have been investigated.The main results are following:（1）The CoAlO catalysts derived from hydrotalcite-like compounds prepared by co-precipitation method were used for acetone catalytic oxidation.Resluts indicated that catalytic activity of CoAlO catalyst firstly increased and then decreased with the increase of Co/Al molar ratios,and decreased with the increase of calcination temperature.5:1 CoAlO catalyst with 5:1 of Co/Al molar ratio and 300oC of calcination temperature had optimal catalytic activity,T_90%=225oC.The catalytic performance of CoAlO catalyst was related with low temperature reducibility,Co³⁺/Co²⁺and O_ads/O_latt.Good crystalline structure of CoAlO catalyst precursor was helpful for improving Co³⁺,O_ads and low temperature reducibility of the catalyst,which was benefited to catalytic oxidation of acetone.（2）CoCeAl-O catalyst was prepared on the basis of Ce into the lattice structure of CoAl hydrotalcite-like compound and used for acetone oxidation.Results indicated that T_90%of acetone conversion on CoAlO and CoCeAl-O catalysts were 238°C and210°C,respectively.The incorporation of Ce improved the low temperature reducibility and active oxygen species.Good low temperature reducibility and abundant active oxygen content were benefited to acetone oxidation on CoCeAl-O catalyst.（3）CoAlO-X catalysts(X=C,S,N and L,they were CO₃^2-,SO₄^2-,NO₃^-and Cl^-,respectivey)were prepared by co-precipitation method and CoAlO-X-Mn catalysts were obtained by the introduction of KMnO₄ on the CoAlO-X catalysts.CoAlO-X and CoAlO-X-Mn catalysts were used for acetone and ethyl acetate oxidation.Results indicated that CoAlO-C and CoAlO-C-Mn catalysts had optimal catalytic activity for acetone and ethyl acetate oxidation,which could be ascribed to good crystalline structure of the catalyst precursor.CoAlO-C-Mn had excellent catalytic activity(T_90%=189oC for acetone oxidation and 180oC for ethyl acetate oxidation)than CoAlO-C-imp Mn prepared by impregnation method,which could be ascribed to the good low temperature reducibility,abundant Co³⁺and adsorbed oxygen species due to the sufficient reaction between KMnO₄ and CoAlO.（4）Co-based catalysts with different morphologies were prepared by first hydrothermal method and secondary hydrothermal method.The catalytic performance and reaction mechanism of flower-like and plate-like catalysts（CoAlO and CoAlO@MnOx）were investigated.Results indicated that the two dimensional structure of plate-like catalysts improved the reaction between acetone molecular and active sites,which is beneficial to acetone oxidation.The P-CoAlO@MnOx catalyst exhibited high catalytic activity,T_90%=204°C,which was ascribed to more Co³⁺and O_adscontent on the plate-like CoAlO@MnOx surface.Besides,catalytic performance of wire Co₃O₄@MnOx catalyst for acetone,ethyl acetate and toluene was investigated.Results indicated that the T_90%of acetone,ethyl acetate and toluene on the Co₃O₄@Mn Ox were 195oC,200oC and 222oC,respectively.The reasons of high catalytic active and high stability of wire Co₃O₄@Mn Ox catalyst were further studied.Results indicated that high catalytic active of Co₃O₄@MnOx catalyst was ascribed to abundant Co³⁺and O_ads on the catalyst surface;High stability of Co₃O₄@MnOx catalyst was ascribed to Co₃O₄@MnOx surface was covered by MnOx,and formed the covering and covered structures structure,which made Co³⁺of Co₃O₄@MnOx catalyst in stable environment.（5）Monolithic catalysts of Ni foam with three-dimensional structure were prepared by hydrothermal method and used for acetone,ethyl acetate and toluene oxidation.Results indicated that the active component of monolithic catalysts were nanoarray morphology and adhered on the surface of Ni foam.The morphology and performance of monolithic catalysts were influenced by hydrothermal time and surfactant.Compared to the Co₃O₄-NF-10 catalyst,the catalytic performance of acetone,ethyl acetate and toluene oxidation on Co₃O₄@MnOx-NF catalyst modified by KMnO₄ was significantly enhanced;T_90%of acetone,ethyl acetate and toluene on Co₃O₄@MnOx-NF catalyst were 177oC,206oC and 237oC,respectively.This could be ascribed to its good low temperature reducibility and synergistic effect between Co and Mn on the catalysts,which were benefited to acetone,ethyl acetate and toluene oxidation on Co₃O₄@MnOx-NF catalyst.