摘要
对于煤制天然气,CO甲烷化技术起着重要作用,其研究核心之一是高效催化剂的开发.目前,CO甲烷化催化剂主要采用金属Ni作为活性组分,但存在高温易烧结和易积炭等问题.因此,如何使其同时具有较高的催化活性和高温稳定性是亟待解决的问题.针对这些问题,本文以高热稳定性的六铝酸镧(La Al11O18)为载体,采用浸渍法担载金属镍,制备了Ni/LaAl_(11)O_(18)催化剂;以高化学惰性的ZrO_2为包覆层,采用改进的连续吸附反应法,将ZrO_2前驱体液相沉积在Ni/LaAl_(11)O_(18)表面进行改性,制备了具有包覆结构的Ni/LaAl_(11)O_(18)@ZrO_2甲烷化催化剂.探讨了ZrO_2在Ni/LaAl_(11)O_(18)表面的分布形式以及不同沉积包覆量对催化剂结构、CO甲烷化催化剂活性和稳定性的影响.分别采用氮气物理吸附、X射线衍射、透射电镜、扫描电镜、氢气程序升温还原、氢气程序升温脱附、X射线光电子能谱、热重分析和电感耦合等离子体原子发射光谱法等手段对催化剂进行了系统表征.结果表明,ZrO_2纳米粒子能够同时分布在催化剂活性组分和载体表面,增加了金属-载体间相互作用力,高温还原时可以有效抑制活性金属Ni的烧结,成功构筑了具有显著限域结构的包覆型催化剂.同时,ZrO_2的包覆不利于金属的氢气化学吸附.在常压,260-600 oC和120 L g^(-1) h^(-1)条件下对催化剂进行了催化活性测试.结果显示,与未改性的催化剂相比,包覆后催化剂上CO转化率略有降低,但是其CH4选择性明显提高,适量的ZrO_2包覆对CH_4得率有较好的促进作用,但是过量的ZrO_2包覆会因占据过多的金属镍表面使得CO转化率显著降低.在常压,550 oC和120 L g^(-1) h^(-1)空速的操作条件下所进行的107 h稳定性测试结果表明,包覆型Ni/LaAl_(11)O_(18)@ZrO_2催化剂展示了良好的高温稳定性,具有优异的抗烧结和抗积碳性能.这主要是因为包覆型催化剂具有良好的'限域'效应,从而显著改善了催化剂的抗烧结性能;同时较强的金属-载体相互作用以及ZrO_2助剂对CO_2的活化提升了催化剂的消碳能力,增强了Ni/LaAl_(11)O_(18)@ZrO_2催化剂的抗积碳能力.总之,本文构筑了一种高稳定性的包覆型催化剂Ni/LaAl_(11)O_(18)@ZrO_2,可广泛应用到其他多种高温反应中.
We report Ni/LaHA@ZrO2catalysts prepared by a facile modified successive adsorption and reaction method for CO methanation.N2adsorption,X‐ray diffraction,transmission electron microscopy,scanning electron microscopy,thermogravimetric analysis,H2temperature‐programmed reduction,H2temperature‐programmed desorption,X‐ray photoelectron spectroscopy,thermogravimetric analysis,and inductively coupled plasma atomic emission spectrometry were used to characterize the samples.The results indicated that the ZrO2nanoparticles were distributed over the surface of the Ni/LaHA@ZrO2catalyst and even partially covered some Ni particles,resulting in the coating exerting a confinement effect.The excess ZrO2had an adverse effect on the enhancement of CO conversion because of the coverage of the surface Ni particles;however,the Ni/LaHA@ZrO2catalyst displayed much higher CH4selectivity than Ni/LaHA because of the activation of the byproduct CO2molecules by ZrO2species.Therefore,even though20Ni/LaHA@ZrO2‐5exhibited similar CO conversion as20Ni/LaHA,the use of the former resulted in a higher CH4yield than the use of the latter.A107‐h‐lifetime test revealed that the Ni/LaHA@ZrO2catalyst was highly stable with superior anti‐sintering and anti‐coking properties because of its coating structure and the promoter effect of ZrO2.
作者
艾红梅
杨洪远
刘庆
赵国明
杨静
古芳娜
Hongmei Ai;Hongyuan Yang;Qing Liu;Guoming Zhao;Jing Yang;Fangna Gu(Key Laboratory of Low Carbon Energy and Chemical Engineering, College of Chemical and Environmental Engineering, Shandong University of Science and Technology, Qingdao 266590, Shandong, China;Assets Management Division, Shandong University of Science and Technology, Qingdao 266590, Shandong, China;State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China)
基金
supported by the National Natural Science Foundation of China (21606146)
Natural Science Foundation of Shandong Province (ZR2016BB17,2016ZRB01037)
Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents (2016RCJJ005,2016RCJJ006)
Government Sponsored Visiting Scholar Foundation of Shandong University of Science and Technology (2016)
Qingdao Postdoctoral Applied Research Project (2015202)
China National Coal Association Science and Technology Research Program (MTKJ2016-266)~~
关键词
六铝酸镧
ZRO2
镍催化剂
包覆结构
CO甲烷化
Lanthanum hexaaluminate
ZrO2
Nickel catalyst
Coating structure
CO methanation
