The Preparation And Characterization Of Co₃O₄ Based Catalysts And The Catalytic Performance Of Methane Combustion

In recent years,energy shortages and environmental pollution have forced people to look for alternatives and cleaner sources of energy.Natural gas is a kind of green,economical,safe and reliable quality energy.Methane,the main component of natural gas,has a greenhouse effect of about 25 times than that of CO₂.The catalytic combustion can completely transform methane at low temperature and avoid environmental pollution.So it is particularly important to prepare highly efficient catalysts for methane catalytic combustion.The catalysts commonly used for catalytic combustion are noble metal and transition metal oxides.Although noble metal catalysts exhibit excellent catalytic activity,its application is limited due to high cost,limited resources and easy sintered at high temperature.However,the transition metal oxide especially Co₃O₄ with spinel structure have widely attracted attentions due to the low price,abundant resources and high thermal stability.In this paper,a series of Co₃O₄ based catalysts were prepared,and the effect of pH values,dispersants and CeO₂ content on methane catalytic combustion were investigated.The catalysts were systematic characterized by means of XRD,SEM,TEM,XPS,Raman and H₂-TPR methods.The main contents were as follows:1.A series of Co₃O₄ catalysts were prepared using precipitation method by changing the pH values at the end point of titration in the preparation process.The results showed that the catalytic performance of the methane combustion first increased and then decreased with the pH values increasing.The Co₃O₄-9.0 catalyst exhibited the most promising activity for methane catalytic combustion,although it has the smallest surface area and biggest crystalline size.The results of XPS and Raman indicated that the surface of Co₃O₄-9.0 catalyst has the highest concentration of A_Tetrahedral/A_Octahedralctahedral and O_ads/O_latt.Therefore,it can be inferred that the higher the Co²⁺concentration of the tetrahedron sites and surface oxygen species,the better performance of methane catalytic combustion.In addition,Co₃O₄-9.0 catalyst has excellent stability and methane conversion rate did not basically decreased after 60 h test.2.In the process of Co₃O₄ catalysts preparation,different dispersants?such as:hexadecyl trimethyl ammonium bromide,sodium acetate,polyethylene glycol?were added so as to enhance the specific surface area of catalysts,and further improve the performance of methane catalytic combustion.However,it was found that the addition of these dispersants did not obviously improve the specific surface area and activity.3.CeO₂?x?-Co₃O₄ catalyst was prepared by co-precipitation method,and the effect of CeO₂ content on the performance of methane catalytic combustion was investigated.It was found that the activity of methane catalytic combustion firstly increased and then decreased with CeO₂ content increasing.When CeO₂ content was10%?x=10?,the catalyst exhibited the best performance for methane catalytic combustion.The XRD results showed that Ce entered the Co₃O₄ lattice and formed a solid solution.Moreover,the introduction of CeO₂ could effectively inhibit the growth of crystalline size.The performance of methane catalytic combustion and characterization results further prove that the concentration of Co²⁺ions and reactive oxygen species concentration on the surface of catalysts play a key role in the methane catalytic combustion.