Preparation Of La-Co Oxides And Its Catalytic Oxidation Of Methane

Ventilation air methane?VAM?in coal mines easily leads to serious environmental pollutions due to the lower concentration and higher emissions of methane.Catalytic combustion is an attractive solution for VAM mitigation and utilization,as the reaction temperature and pollutant emission can be reduced.LaCoO₃ oxides have attracted wide attention in the field of homogeneous catalysis due to its excellent thermal stability,electron mobility and redox ability.However,the preparation of LaCoO₃ oxides requires high-temperature calcination,which easily leads to agglomeration of LaCoO₃ particles,resulting in low catalytic activity.In this work,we successfully synthesize the high performance La-Co oxides with a high specific surface area and excellent redox ability by means of surface modification,structure regulation and component regulation.1)Mg doped and coated LaCo_1-xMg_xO₃ and LaCoO₃@MgO-y?x,y=0.1,0.2,0.3?core-shell catalysts are successfully prepared by sol-gel method.The surface acid-base properties of LaCoO3 is modified by alkaline earth oxide MgO,and its effect on the catalytic performance of methane was explored.The MgO shell nanostructure of the catalyst cause a great change in the number and distribution of acid-base sites on the surface of LaCoO₃,which alters the adsorption capacity of methane on LaCoO3 surface and its catalytic reaction pathway.The stability test of LaCoO₃@MgO-0.1 catalyst shows high activity after working for 100 hours.2)A series of Co/Fe-modified LaCoO_3-xCo?x=0-20%?and LaCoO3-x Fe?x=1-10%?catalysts named LC-Co and LC-Fe are fabricated by hydrothermal method using LaCoO₃?prepared by sol-gel method?as precursor.The microstructure of LaCoO₃ is modified by adding transition metals through the hydrothermal recrystallization process.When 2%Co or 7%Fe is added,LC-2Co and LC-7Fe exhibit the best methane catalytic activity.The specific surface area,pore volume and pore diameter of the two catalysts,as well as the content of lattice oxygen and Co²⁺on the surface of the catalysts,all significantly improve the catalytic performance of methane.3)La-Co composite catalyst named LC-DES-x h?x=2,4,6?are synthesized by a facile hydrothermal route with the help of deep eutectic solvents?DES?using LaCoO₃?prepared by solution combustion method?as precursor.The composite phases are La2O2CO3,LaCoO3 and Co3O4 catalysts,respectively.When the hydrothermal time is 6 h,hydrothermal temperature is 230?,solvent addition is 5 mL and calcination temperature is600?,the catalyst exhibits the best activity.The excellent catalytic performance of the LC-DES-6h catalyst is attributed to the rich pore structure,excellent redox ability and the formation of C-O bonds between three phases.Two catalytic cycles and stability test of LC-DES-6h catalyst shows high activity after working for 72 hours.