Study On The Synergistic Effect Of Methane Combustion Catalyzed By MO-MCo₂O₄（M=Cu、Ni） Composite System

Due to the massive development and utilization of fossil energy,carbon dioxide emissions are increasing rapidly,causing serious environmental pollution and carbon emission control is becoming more and more urgent,for which people put forward dual carbon targets（carbon emission peak and carbon neutrality）for pollution reduction.Methane,which has large reserves and low carbon emissions per unit of energy,can be selected as an energy source to greatly reduce the pressure of carbon emissions in the energy industry.Methane is the second largest greenhouse gas on earth after carbon dioxide,and its greenhouse effect is more than twenty times that of carbon dioxide.Reducing the emission of unburned methane is beneficial to reduce environmental pollution.Catalytic combustion is considered to be an effective way to improve the efficiency of methane combustion.Catalytic combustion can both reduce the temperature of methane combustion and reduce the emission of pollutant gases such as nitrogen oxides due to high temperature combustion,which largely improves energy efficiency and reduces pollutant emissions.Therefore,it is of urgent practical value to carry out research on catalytic combustion of methane.Currently,methane catalysts have been studied for two main categories:noble metals and transition metal oxides.The noble metal catalysts have been shown to exhibit high activity for methane catalysis,but they are unstable and easily deactivated at high temperatures and have scarce reserves.Transition metal oxide systems not only have large reserves of raw materials and low prices,but also have high thermal stability and excellent catalytic activity.Therefore,transition metal catalysts with spinel structure are considered to be the most promising catalysts to replace noble metals.In this paper,a series of MO-MCo₂O₄（M=Cu,Ni）mixed oxide catalysts were prepared by a soft chemical method,characterized by XRD,SEM,BET,Raman and XPS,and their catalytic performance for methane combustion was investigated to explore the synergistic effect of the mixed oxides.The main studies are as follows:（1）The spinel-based（Cu O）_x-Cu Co₂O₄（x=0,0.1,0.2）mixed oxide catalysts were synthesized by the solvothermal method,and the performance of（Cu O）_x-Cu Co₂O₄ mixed oxide catalysts for methane combustion was investigated.XRD results demonstrated the coexistence of Cu O and Cu Co₂O₄ phases in our synthesized samples.SEM and EDX spectra showed that the mixed oxides are uniformly distributed particles on the nanometer scale.The catalytic results show that the activity of all catalysts for methane catalytic combustion is in the order of（Cu O）_0.2-Cu Co₂O₄>（Cu O）_0.1-Cu Co₂O₄>Cu Co₂O₄>Cu O.it can be seen that the catalytic activity of Cu Co₂O₄ composite oxide increases with the increase of Cu O content.The Cu⁺/Cu²⁺ratio was calculated based on the XPS pattern fitting and the results are as follows,the ratio of Cu⁺/Cu²⁺was 0.48 in Cu Co₂O₄ and 0.53in the（Cu O）_0.2-Cu Co₂O₄ mixed oxide.It indicates that the Cu⁺content in the Cu Co₂O₄spinel oxide increased after the addition of Cu O and the mixed oxides with abundant defects and surface ionic valence increased the number of oxygen vacancies and improved the catalytic activity.This was due to the addition of Cu O,which increased the number of oxygen vacancies and oxygen exchange capacity on the surface of the Cu Co₂O₄ composite oxide,exhibiting an obvious synergistic catalytic effect.（2）The spinel-based（Ni O）_x-Ni Co₂O₄（x=0,0.1,0.2）mixed oxide catalysts were synthesized by hydrothermal method,and the catalytic performance of（Ni O）_x-Ni Co₂O₄mixed oxides for methane combustion was investigated.The XRD results verified that the samples we synthesized were the desired（Ni O）_x-Ni Co₂O₄ composite oxides.The morphological characteristics of the samples were observed by SEM images and all sample particles were all the sample particles were tightly and uniformly distributed on the surface,with good dispersion and no large aggregation or separation.XPS results showed that the surface of the composite oxide samples possessed abundant surface valence and defects,which could enhance the oxygen mobility in the catalytic reaction.In addition,the addition of Ni O replaces part of Co,which may improve the oxygen exchange capacity of methane oxidation.The results of catalytic activity tests showed that Ni O has a positive effect on the enhancement of the catalytic methane activity of Ni Co₂O₄.Combined with other characterization techniques,it was shown that Ni O and Ni Co₂O₄ showed synergistic effects in catalytic methane combustion,which made the catalytic combustion reaction of methane easier at low temperatures under the combined effect of Ni O and Ni Co₂O₄.