Preparation Of Transition Metal Oxide Catalysts With High Moisture Resistance And Activity And Their Performance For Catalytic Combustion Of Toluene

Catalytic combustion is one of the effective techniques for the destruction of VOCs. One of the prominent problems is that the presence of water vapor had a negative effect on catalytic activity, and thus decreased the degradation efficiency of VOCs. Therefore, the studies of non-noble metal catalysts with high activity and moisture resistance is great important for the destruction of VOCs under conditions of high humidity.In order to solve the problem about catalyst deactivation in high humidity circumstance, the effect of surface chemical properties of the catalysts on their activity and moisture resistance was studied. The novel transition metal oxide catalysts with high moisture resistance and activity were prepared from the technical level.The activity of the catalysts CoOx/Cordierite, MnOx/Cordierite and CrOx/Cordierite for toluene oxidation was investigated. The results showed that the activity of the catalyst CoOx/Cordierite was the highest among the three catalysts. The catalyst CoOx/Cordierite-EG prepared by chemical reduction with ethylene glycol had the better activity than the catalyst CoOx/Cordierite prepared by impregnation method. It was mainly attributed to the cobalt (II) species with better dispersion presented on the CoOx/Cordierite-EG catalyst. This is one of the innovations in this work.The influence of water vapor on the catalytic activity of the catalysts CoOx/Cordierite, MnOx/Cordierite and CrOx/Cordierite for toluene oxidation was investigated. The presence of water vapor had a negative effect on the catalytic activity. It was mainly attributed to the competition of water molecules with toluene molecules for adsorption on the active sites. The degree of degradation in the catalytic activity of the catalysts due to presence of water vapor followed the order:CoOx/Cordierite> MnOx/Cordierite> CrOx/Cordierite. H2O-TPD studies showed that the strength of interactions between water molecules with the surface of the catalyst CrOx/Cordierite was weaker than the other two catalysts. As a consequence of that, CrOx/Cordierite exhibited the best durability to water vapor among the three catalysts.In order to further improve the catalytic performance, various transition metals (Mn、Ce、 Fe%Cr) were separately added to the catalyst CoOx/Cordierite. The results showed that the dopping of Ce or Mn on the catalyst CoOx/cordierite can improve its durability towards water vapor poisoning. H2O-TPD showed that the interaction between water molecules with the surface of CoCe(0.4)Ox/cordierite was the weakest. As a result, this catalyst had the best moisture resistance. The dopping of Ce on the catalyst CoOx/cordierite can result in an increase in its Co2+content and a decrease in its Co3+content, which weakened adsorption of the catalyst surface towards water vapor, and thus increased the durability to water vapor. The conversion of toluene on the catalyst CoCe(0.4)Ox/cordierite maintained stabilization when relative humidity varied from55%to90%. The durability of the catalyst CoCe(0.4)Ox/cordierite towards water vapor was much better than that of the catalysts reported in the literatures. This is one of the innovations in this work.The bimetallic catalysts CuMn(y)Ox/y-Al2O3were prepared, and their catalytic activity for the toluene oxidation was examined. The results showed that the activity of the bimetallic catalysts was higher than that of the monometallic catalysts CuOx/γ-Al2O3and MnOx/γ-Al2O3. The activity of CuMn(1)Ox/γ-Al2O3was the best among these catalysts, and its T90, the temperature required for90%toluene conversion, was229℃. It was mainly attributed to the formation of the phase Cu1.5Mn1.5O4in the bimetallic catalyst CuMn(1)Ox/γ-Al2O3. This is one of new points in this work.The catalytic combustion kinetics of toluene over the catalyst CuMn(1)Ox/γ-Al2O3was investigated. The results showed that MVK model based on redox mechanism was suitable to describe the catalytic combustion kinetics of toluene over CuMn(1)Ox/γ-Al2O3.Copper and manganese based catalysts with different supports were prepared. The effect of water vapor on the activity of the catalysts for toluene oxidation was investigated. The degradation of the catalytic activity of the catalysts by water vapor followed the order: CuMn(1)Ox/γ-Al2O3> CuMn(1)Ox/TiO2> CuMn(1)Ox/Cordierite. H2O-TPD studies showed that the strength of interactions between water molecules with the surfaces of the three catalysts followed the order:CuMn(1)Ox/γ-Al2O3> CuMn(1)Ox/TiO2> CuMn(1)Ox/Cordierite. As a consequence of that, CuMn(1)Ox/Cordierite exhibited the best durability to water vapor. This is one of new points in this work.The catalysts MnCe(y)Ox/TiO2were prepared and their catalytic activity for toluene oxidation was investigated. The results showed that the catalyst MnCe(0.1)Ox/TiO2had higher activity and better durability towards water vapor than other catalysts MnCe(y)Ox/TiO2tested. It is ascribed to the higher dispersion of manganese species on the support. This is one of the innovations in this work.The ternary metal oxide catalysts CuMnCe(y)Ox/TiO2were prepared, and their catalytic activity for toluene oxidation was investigated. The results showed that when Cu:Mn:Ce molar ratio=1:1:0.25, the prepared catalyst CuMnCe(0.25)Ox/TiO2exhibited the best activity among the catalysts tested. Under the condition (Toluene concentration=5.956g/m3, GHSV=23000h-1), its T90, the reaction temperature required for90%toluene conversion, was only 201℃. The activity of the CuMnCe(0.25)Ox/TiO2was better than that of the non-noble metal catalysts, and reached or come close to that of the noble metal catalysts reported in the literatures. This is one of the innovations in this work.