【作者】 刘洁；

【导师】 段二红； 王赛飞；

【作者基本信息】 河北科技大学 ， 环境科学与工程， 2019， 硕士

【摘要】 通风空气甲烷,俗称“乏风”,由于浓度低,排放量大造成了严重的环境污染问题。甲烷的催化燃烧可以在相对较低的温度下转化轻烃,降低污染物排放,燃烧效率比较高。LaCoO₃氧化物具有优异的热稳定性、电子迁移率和氧化还原能力,使其在多相催化领域获得了广泛关注。但是LaCoO₃制备过程需要高温焙烧,易造成颗粒团聚,导致其催化活性较低。本文旨在通过表面改性、结构调控、组分调控三方面入手来制备大比表面积、强氧化还原能力的高性能La-Co氧化物。1)利用溶胶凝胶法成功制备了碱土金属Mg掺杂和涂覆的LaCo_1-xMg_xO₃、LaCoO₃@MgO-y（x,y=0.1,0.2,0.3）催化剂。通过调控表面酸碱性质探究Mg改性的LaCoO₃催化剂对甲烷催化性能的影响。MgO壳纳米结构引起LaCoO₃表面酸碱性位点的数量和分布发生较大变化,改变了甲烷在LaCoO₃表面的吸附能力及其催化反应途径。当涂覆或掺杂10%Mg时,催化剂具有最好的甲烷催化性能。对LaCoO₃@MgO-0.1催化剂进行稳定性实验,经100h依然保持着良好的催化性能。2)以溶胶凝胶法制备的LaCoO₃为前驱体,利用水热法制备了过渡金属Co、Fe改性的LaCoO₃-x Co（x=0-20%）和LaCoO₃-y Fe（y=1-10%）催化剂,记为LC-x Co和LC-y Fe。通过在水热过程添加金属离子促使LaCoO₃晶体重新结晶,并同步实现其微观结构调控。当添加2%Co、7%Fe时,LC-2Co和LC-7Fe催化剂具有最好的甲烷催化性能。两种催化剂的比表面积、孔容孔径以及表面晶格氧和Co²⁺含量均显著提高,较大程度提升了甲烷催化性能。3)以溶液燃烧法制备的LaCoO₃为前驱体,利用低共熔溶剂（DES）辅助的水热法制备了La-Co复合催化剂,其物相组成为LaCoO₃/La₂O₂CO₃/Co₃O₄三相,记为LC-DES-x h（x=2,4,6h）。当制备条件为水热6h、水热温度230℃、溶剂添加量为5mL和焙烧温度为600℃时,催化剂具有最好的甲烷催化性能。LC-DES-6h优异的催化性能归因于该复合物丰富的孔道结构、优异的氧化还原能力以及三相之间C-O键的形成;对LC-DES-6h进行两次催化反应循环及稳定性实验,经72h依然保持着良好的催化性能。更多还原

【Abstract】 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.更多还原