Experimental Study On Catalytic Oxidation Of Volatile Organic Compounds By Co-Mn-Ce Composite Oxides

Volatile Organic Compounds?VOCs?are mainly derived from industrial production and vehicle exhaust emissions.Their reaction with NO_x under the action of sunlight can cause a series of air pollution problems.Catalytic oxidation technology is considered as one of the most reliable methods,and the key is to improve oxidation performance.The non-precious metal Co-Mn-Ce composite oxide catalysts have advantages of high activity and low cost.Therefore,improving the performance of low-temperature oxidation VOCs has good significance and application value.A series of homogeneous VOCs catalysts with different Mn contents were prepared by co-precipitation method:the molar ratio of Co/Mn/Ce was 3:x:2?x=1,3,5,7?.The morphology,structure and redox capacity of the catalyst were analyzed using characterization technology.Based on the gas test platform,the propane oxidation performance of catalysts with different Mn contents was evaluated.Besides,the effects of reaction conditions on the optimal catalyst propane oxidation were carried out.Finally,the effects of NO on the oxidation performance of propane and propene were investigated.The main research contents are as follows:?1?A series of VOCs catalysts were prepared by precipitation method:Co/Mn/Ce molar ratio was 3:x:2?x=1,3,5,7?.X-ray Diffraction?XRD?,X-ray Photoelectron Spectroscopy?XPS?,Electron Paramagnetic Resonance?EPR?,and H₂ Temperature Program Reduction?H₂-TPR?.The crystal phase structure,element valence,oxygen vacancy and redox capacity of the catalyst were characterized.The results showed that the Co-Mn-Ce catalysts mainly existed in the form of CeO₂ cubic fluorite,and no specific Mn diffraction peak was observed with the increase of Mn content.The Mn element in the catalyst coexisted as Mn²⁺,Mn³⁺and Mn⁴⁺.When x=1,the Co-Mn-Ce catalyst has the smallest grain size,and the maximum ratio of Mn⁴⁺/(Mn²⁺+Mn³⁺+Mn⁴⁺)was 0.375.Besides,the catalyst exhibited good redox capacity.?2?The test platform was used to evaluate the propane oxidation capacity of a series of catalysts with different Mn contents under different water atmospheres.Based on this,the optimal catalyst was selected and the reaction temperature,propane concentration,O₂ concentration and water vapor concentration effected on propane oxidation.The results showed that the order of oxidation performance was:CMC-1>CMC-7>CMC-5>CMC-3.The oxidation performance of Co-Mn-Ce catalysts were greatly affected by temperature.When x=1,the oxidation performance was the best,and it reached the ignition temperature(T₁₀)at 200?,with better low temperature performance.In addition,temperature had the greatest influence on the oxidation performance of the catalyst.It limited the oxidation of propane by CMC-1 catalyst without oxygen.when the concentration of water vapor increased to 10 vol%,it inhibited propane oxidation,resulting in the increase of the complete oxidation temperature.Finally,based on the mechanism of L-H reaction,a three-step reaction path of adsorption,partial oxidation and complete oxidation was constructed.?3?VOCs/O₂/H₂O and VOCs/O₂/H₂O/NO atmosphere constant temperature oxidation tests were carried out through the gas test platform,and the changes of VOCs?propane and propene?,NO and water vapor concentration reaction conditions on the reaction components were investigated influences.The results showed that propane oxidation capacity of CMC-1 catalyst improved as the temperature increased.When the reaction temperature was 300?,the introduction of NO could obviously inhibit the oxidation of propane.Under the condition of 0 vol%water vapor,the conversion rate of propane decreased by 4.5%after passing NO.Under the condition of 5 vol%water vapor,the propane conversion decreased from 80%to 66.8%after the introduction of NO.Under the condition of 10 vol%water vapor,the propane conversion decreased from 40.6%to 33.3%after the introduction of NO.As the temperature increased,the NO inhibitory effect on propane oxidation decreased.Replace propane with propene in the reaction feed.When the reaction temperature was 200?,NO had an inhibitory effect on the oxidation of propane,and the change rule of each gas component was similar to the above.