Experiment On Synthesis Of Mn-Ce Catalyst By The Redox-precipitation Method And Catalytic Performance For Lean Methane Combustion

Methane is the second greenhouse gas.The direct emissions of low-concentration methane from coal mine gas and automobile exhaust not only seriously pollute the environment but also waste energy.Due to the advantage of the lower light-off temperature,the higher conversion efficiency and the stabler combustion process,catalytic combustion is an ideal treatment technology for low-concentration methane.The advantages of lower price and excellent thermal stability have attracted the attention of researchers,and Improving the performance is the key to promoting the application of transition metal catalysts.In this paper,Mn-Ce catalysts were synthesized by the redox-precipitation method,and the catalytic performance were studied for low-concentration methane.the ratio of Mn-to-Ce,the synthesis methods and the sulfur-resistant of the catalyst were studied,too.The catalysts were characterized for the physicochemical properties by XRD,BET,XRF,SEM,and XPS etc,explaining the reason that the optimal the ratio of Mn-to-Ce for the catalyst synthesized by the redox-precipitation method is higher than the literature and the excellent sulfur resistance from the microcosmic aspect.The catalysts synthesized by the redox-precipitation method not only had relatively better catalytic performance,but also had the higher ratio of Mn-to-Ce（9/1）than that of the literature.The results of Characterization show that K_xMn₈O₁₆ was one of the main active phases,resulting in the optimalest ratio of Mn-to-Ce highering than the literature.The Mn-Ce catalysts synthesized by the redox-precipitation method had the larger specific surface area and the larger pore volume providing more active sites and promoting the diffusion of the reactants in the catalyst,and had higher concentration of Mn⁴⁺,Ce³⁺,and O_α on the surface promoting the activation of methane and oxygen on the catalyst surface.The K element in the catalysts weakened the Mn-O bond promoting the transformation of Mn₃O₄ to Mn O and improving its redox performance.The changes of the phase and the micro-morphology before and after the reaction indicated that the SO₂ poison for the catalyst is to convert the active phase(K_xMn₈O₁₆ and Mn₅O₈)into Mn₃O₄ with lower methane catalytic activity and manganese sulfate without methane catalytic activity.The excellent sulfur resistance of the catalysts synthesized by the redox-precipitation method was due to the excellent SO₂ chemisorption strength and capacity of K_xMn₈O₁₆.The catalyst in upstream of the catalytic system was used to remove SO₂ from the reaction gas,and the catalyst in downstream was protected from poisoned by SO₂,improving the total life and performance of the catalytic system.Further,we proposed an idea to enhance the overall performance of the catalytic system,which is that placing the highly chemisorption strength and capacity device of SO₂ at the upstream of the catalytic system to remove SO₂ from coal mine gas and automobile exhaust,reducing the influence of SO₂ for catalyst,and improving the life of the catalytic system.