催化学报

催化学报 ›› 2020, Vol. 41 ›› Issue (7): 1140-1151.DOI: 10.1016/S1872-2067(20)63544-6

• 论文 • 上一篇    下一篇

基于FeWOx/SiO2载氧体的甲烷化学链部分氧化反应

刘蕊a,b, 裴春雷a,b, 张先华a,b, 陈赛a,b, 李洪芳a,b, 曾亮a,b, 慕仁涛a,b, 巩金龙a,b   

  1. a 天津大学化工学院绿色合成与转化教育部重点实验室, 天津 300072;
    b 天津化学化工协同创新中心, 天津 300072
  • 收稿日期:2019-09-30 出版日期:2020-07-18 发布日期:2020-04-18
  • 通讯作者: 巩金龙
  • 基金资助:
    国家重点研发计划（2016YFB0600901）；国家自然科学基金（51761145012，21525626，U1663224）；高等学校学科创新引智计划（B06006）.

Chemical looping partial oxidation over FeWOx/SiO2 catalysts

Rui Liua,b, Chunlei Peia,b, Xianhua Zhanga,b, Sai Chena,b, Hongfang Lia,b, Liang Zenga,b, Rentao Mua,b, Jinlong Gonga,b   

  1. a Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China;
    b Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China
  • Received:2019-09-30 Online:2020-07-18 Published:2020-04-18
  • Supported by:
    This work was supported by the National Key R&D Program of China (2016YFB0600901), the National Natural Science Foundation of China (51761145012, 21525626, U1663224), and the Program of Introducing Talents of Discipline to Universities (B06006). We also acknowledge the financial support from China National Petroleum Corporation for this research.

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摘要： 甲烷具有价格低廉且储量丰富的优点,因此将甲烷转化为合成气(一种H2:CO为2的混合物),从而进一步合成有价值的化学品和液体燃料引起了人们的极大关注.化学链甲烷部分氧化(CLPOM)技术能避免甲烷与空气直接接触而引起爆炸的危险,可以降低后续对合成气与氮气分离操作所带来的费用,因此日益受到关注.CLOPM过程主要分为两步:第一步,CH4被载氧体所携带的氧部分氧化,载氧体被还原;第二步,利用氧化剂(例如空气)将被还原的载氧体再氧化恢复.因此,载氧体在CLOPM过程中起到至关重要的作用.载氧体的选择主要存在两个问题:(1)甲烷被活化所产生含碳产物的能力与晶格氧的给氧能力不匹配所带来的严重碳沉积;(2)金属离子间扩散速率不匹配而造成载氧体在氧化还原过程中结构的不可逆变化.基于上述两个问题,本文设计了FeWOx/SiO2载氧体用于CLPOM.与未改性的WO3/SiO2载氧体相比,甲烷的转化率和合成气的收率都有显著提高.FeWOx/SiO2在900℃、1 atm反应条件下表现出62%的甲烷转化率、93%的CO气相选择性、94%的H2选择性和2.4的H2/CO比值,同时在50个循环中表现出优异的催化活性和稳定性.本工作利用CH4脉冲反应研究了FeWOx/SiO2的甲烷表面反应过程;采用CH4-TPR和H2-TPR相结合探究了甲烷活化速率与晶格氧扩散速率之间的关系;通过XPS和XRD对FeWOx/SiO2在氧化还原过程中的结构稳定性进行了探讨.综合上述实验结果,对FeWOx/SiO2应用于CLPOM的反应机理进行了阐述.
H2-TPR结果表明,在FeWOx/SiO2中,相较于Fe2O3/SiO2,Fe-O的活性受到抑制,使其更倾向于与甲烷发生部分氧化反应;相较于WO3/SiO2,W-O的活性得到明显提升,因此更多的晶格氧可以参与到部分氧化反应中来氧化积碳,从而使合成气收率大幅度提升.从CH4-TPR结果可以看出,对于FeWOx/SiO2,CO与H2的生成温度最接近,意味着晶格氧的传输速率较快并且能够与甲烷活化产生含碳中间物种的速率相匹配,将其及时氧化生成CO,避免由于积碳造成的催化剂失活.
结合XPS和XRD结果可以得出,在甲烷还原过程中,FeWOx经历一步还原形成Fe-W合金,由于其间存在强相互作用,因而抑制了还原过程中催化剂相分离现象的发生.同时,根据铁钨离子在空气条件下扩散速率的公式计算可以得出,其相近的离子氧化速率也保证了在氧化过程中催化剂结构的稳定性.本工作为进一步构建用于甲烷化学链部分氧化制合成气的复合金属氧化物载氧体提供了研究思路.

关键词: Fe-W合金, 甲烷活化, 晶格氧扩散, 相分离, 离子氧化速率

Abstract: This paper describes the design of a FeWOx-based oxygen carrier for the chemical partial oxidation of methane (CLPOM). Thermodynamic screening and kinetic analyses both forecast the FeWOx-based oxygen carrier as a promising candidate for the production of syngas. The total methane conversion and syngas yield can be dramatically increased with this catalyst compared to the case with the unmodified WO3/SiO2, thereby enabling CLPOM with 62% methane conversion, 93% CO gas-phase selectivity, 94% H2 selectivity, and a 2.4 H2/CO ratio. The catalyst has the advantages of high availability of lattice oxygen to oxidize carbonaceous intermediates in time, together with the formation of an Fe-W alloy to promote the surface reaction. Consequently, it demonstrates excellent catalytic performance with no catalyst deactivation at 900 ℃ and 1 atm. The excellent structural stability plays an essential role in CLPOM. As revealed via XPS and ICP, the phase segregation has not been observed due to the strong interaction between Fe and W, which resulted in the formation of the Fe-W alloy during the reduction processes and the match between the ion oxidation rates of the Fe and W ions in the oxidation stage. The results provide fundamental information on the reaction mechanism of FeWOx/SiO2, and present it as a promising candidate for CLPOM.

Key words: Fe-W alloy, Methane activation, Lattice oxygen diffusion, Phase segregation, Ion oxidation rate