Co-doped OMS-2 Catalysts And Their Catalytic Activities For Deep Catalytic Oxidation Of O-xylene

Benzene hydrocarbon,such as benzene,toluene and xylene,belongs to volatile organic compounds（VOCs）,which is one of the major air pollutants and it mainly comes from the production of chemical raw materials,automobile exhaust emissions and home decoration,etc.VOCs can cause serious damage to the ecological environment and great harm to human health.Catalytic combustion is one of the best methods to govern VOCs and the creation of high efficient catalyst serves as the vital role in governing VOCs.The dissertation mainly describes a series of catalysts with excellent performance and lower temperature.They have been developed with regarding o-xylene catalytic as the objective pollutant.The experiment results are as follows:（1）KMnO₄ as oxidant,Mn（Ac）2、Mn（Ac）2 as reducing agent,in this way we get the catalyst named 0.06Co-OMS-2-400,XCo-OMS-2-Y-Z for short.X represents the mole ratio of Co/Mn.Y represents the solution concentration of Co（CH3COO）₂.Z represents the calcination temperature.Then we make a comparison among 0.06Co/OMS-2-400 making by the method of impregnation OMS-2-400 which worked as blank sample and 0.06 Co-OMS-2-400.The test result of the o-xylene’s catalysis show,the T100（The catalytic combustion temperature of the CO2 when the productivity is 100%）of the 0.06Co-OMS-2-400 is 200℃.Compared with the 0.06Co/OMS-2-400 making by the method of impregnation,and OMS-2-400 which worked as blank sample,the T100 of the 0.06Co-OMS-2-400 lowers 20 and 10℃ ℃ respectively.The T20 of the 0.06Co-OMS-2-400 is 130℃,which declines 45 ℃and 36℃ respectively compared with the 0.06Co/OMS-2-400 and OMS-2-400.So as we can see,using the redox precipitation to doping the cobalt is favorable to raise the high temperature and low temperature catalytic activity of the catalyst.The characteristics of XRD structure shows that,The Mn in the catalysts developed by the two methods exists as the form of Mn O2,and the Co exists in the form of Co3O4.However,the catalyst prepared by the impregnation method has the characteristic of absorption peak of Co3O4 but the catalyst prepared by the oxidation-reduction method doesn’t have.After the text of EDX,the catalyst obtained by the redox precipitation contains the Cobalt element.It is suggested that the redox precipitation method may disperse cobalt species in the gap of OMS-2 lattice.And the BET test shows that,the specific surface area of the 0.06Co-OMS-2-400 can reach 129.452m²/g,which is much greater than 0.06Co/OMS-2-400（49.196m²/g）and OMS-2（60.447m²/g）.The result of the SEM shows that,the morphology of 0.06Co-OMS-2-400 is the regular tetragonal particles.The morphology of 0.06Co/OMS-2-400 is a mass of nanoparticles.The morphology of OMS-2 is massive particle which varies in size.The test of H2-TPR shows that,the lowest temperature of 0.06Co-OMS-2-400 reduction peak can reach 288℃,which reduces 38 ℃compared with OMS-2-400 and reduces 49 ℃compared with 0.06Co/OMS-2-400.These results indicate that,the catalytic activity of the Co doped OMS-2 catalyst obtained by the redox precipitation method is likely to be that the cobalt enters into the lattice of OMS-2,and it increases the distance between the Mn-O keys,so the specific surface area of it is maximum.Further more,the cobalt ions in the 0.06Co-OMS-2-400 promotes the exchange of Mn3+/Mn4+,which is good for the catalytic oxidation of o-xylene into CO2 and H2 O.In the catalytic oxidation of o-xylene activity test,the T100 of 0.06Co-OMS-2-0.7-400 is 200℃,and the T20 is 130℃,so it is the best catalytic activity.（2）For the further research in redox precipitation method,the molar ratio of cobalt and manganese,concentration of cobalt acetate solution and calcination temperature were changed.The results showed that the catalyst with Co/Mn molar ratio of 0.06,concentration of cobalt acetate solution 0.7mol/L and calcination temperature 400 could ℃complete catalytic oxidation of o-xylene at 200 ℃due to cobalt species highly dispersed into the lattice of manganese oxide,which can effectively activate lattice oxygen and obviously improve the catalytic properties of the catalysts.（3）When the acid group(CH₃COO^-,NO₃^-,SO₄^2-)of manganese salt and cobalt salt are changed respectively,XRD results show that the crystal form of acid radical is OMS-2 at changed after and not before.The results of BET test show that when the acid is CH₃COO^-,the specific surface area is 129.452m²/g;when the acid is SO₄^2-,the specific surface area is 58.608m²/g;group NO₃^-,the specific surface area is 46.757m²/g;XRD results show that only when the acid is CH₃COO^-,crystal is clear and without diffraction peaks of Co3O4.SEM results show that the catalyst is prepared from acetic acid radical is as the reactants,its appearance is the tetragonal morphology of the particle distribution.The results of H2-TPR show that the lowest temperature of the reduction peak of cobalt manganese composite catalyst 0.06Co-OMS-2-0.7-400 is prepared by acetic acid.The results show that the catalytic activity of the catalyst prepared by the reaction of acetic acid to the cobalt manganese composite catalyst differently was the largest.At 200 the cobalt ℃manganese composite catalyst can catalyze oxidation of o-xylene completely.