镧系金属掺杂MCM-41的合成、表征及其脱硝性能研究

Synthesis, characterization,and de-NO_x performance of lanthanum-doped MCM-41

以正硅酸乙酯、硝酸镧、硝酸铈为原料,十六烷基三甲基溴化铵作模板剂,水热条件下合成镧、铈掺杂介孔分子筛。采用XRD、FT-IR和氮气吸附脱附等对镧系金属掺杂MCM-41进行表征,并以氨为还原剂研究其选择性催化还原一氧化氮活性以及反应条件(包括镧系掺量、反应温度、空速、氨氮比等)对催化性能的影响。本文旨在掺杂镧系金属提高分子筛的脱硝性能。镧系掺杂的分子筛改变了骨架增强了反应活性,稀土金属的高电荷密度使分子筛催化活性提高。结果表明,镧系金属镧、铈成功进入MCM-41介孔材料的骨架内并保持有序的六方介孔结构,随着镧系掺杂量的增加,介孔有序性降低。当n(镧系金属)/n(硅)=0.04、空速为4 000 h-1、n(氨气)/n(一氧化氮)为1时Ln-MCM-41催化剂在350℃反应时能保持较高活性。镧系掺杂的介孔分子筛能更有效地提高催化性能。

Abstraet：Using tetraethylorthosilicate （TEOS）,lanthanum nitrate, and cerium nitrate as raw materials and cetyl-trimethylammonium bromide （CTMAB） as the template agent, MCM-41 mesoporous molecular sieves were synthesized with La or Ce incorporated in the framework under hydrothermal conditions.The structure and the state of Ln-doped MCM-41 were characterized by the analysis of XRD, FT-IR, and nitrogen adsorption-desorption.Its activities of selective catalytic reduction of NO with ammonia as reductant as well as the influences of lanthanide doping content, temperature, space velocity and n （NH3）/ n （NO） on catalytic performance were investigated.The aim of this work was to incorporate lanthanide to improve de-NO, performance of molecular sieves.Ln-MCM-41 changed skeleton structure ,which could increase the number of lattice defects to improve reactivity and pore surface adsorption due to exchangeability of rare earth metal ions.The result indicated that La and Ce were introduced into the framework of MCM-41 mesoporous materials and maintained an orderly hexagonal pore structure.The order degree declined with the increase of La and Ce doping amounts.Ln-MCM-41 could maintain high activity at 350℃ when n （ Ln ）/n （Si） =0.04, space velocity was 4 000 h-1 , and n （NH3）/n （ NO ） = 1：1 .The lanthanide-doped MCM-41 molecular sieves will be helpful in promoting catalyst activity effectively. Key words： mesoporous molecular sieves ;Ln-MCM-41 ;selective catalytic reduction