物理化学学报 >> 2019, Vol. 35 >> Issue (9): 1027-1036.doi: 10.3866/PKU.WHXB201902004

所属专题: 碳氢键活化

论文 上一篇    

固体酸WO3/TiO2负载锂锰催化剂组成对其甲烷氧化偶联反应性能的影响

程飞1,2,杨建1,*(),闫亮1,赵军1,赵华华1,宋焕玲1,丑凌军1,3,*()   

  1. 1 兰州化学物理研究所,羰基合成与选择氧化国家重点实验室,甘肃 兰州 730000
    2 中国科学院大学,北京 100049
    3 中国科学院兰州化物所苏州研究院,江苏 苏州 215123
  • 收稿日期:2019-02-01 录用日期:2019-03-06 发布日期:2019-03-08
  • 通讯作者: 杨建,丑凌军 E-mail:yjian@licp.cas.cn;ljchou@licp.cas.cn
  • 基金资助:
    中国石油科技创新基金(2016D-5007-0506);中国科学院战略性先导科技专项(XDA09030101)

Influence of the Composition/Texture of Solid Acid WO3/TiO2-Supported Lithium-Manganese Catalysts on the Oxidative Coupling of Methane

Fei CHENG1,2,Jian YANG1,*(),Liang YAN1,Jun ZHAO1,Huahua ZHAO1,Huanling SONG1,Lingjun CHOU1,3,*()   

  1. 1 State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China
    2 University of Chinese Academy of Sciences, Beijing 100049, P. R. China
    3 Suzhou Research Institute of LICP, Chinese Academy of Sciences, Suzhou 215123, Jiangsu Province, P. R. China
  • Received:2019-02-01 Accepted:2019-03-06 Published:2019-03-08
  • Contact: Jian YANG,Lingjun CHOU E-mail:yjian@licp.cas.cn;ljchou@licp.cas.cn
  • Supported by:
    The project was supported by the Petro China Innovation Foundation(2016D-5007-0506);the "Strategic Priority Research Program" of the Chinese Academy of Sciences(XDA09030101)

摘要:

甲烷氧化偶联制乙烷、乙烯是一种最直接有效的甲烷转化工艺路线。催化剂的结构、碱性、活性组分的状态及分布和氧物种的性质是影响甲烷氧化偶联性能的重要因素,而这些因素与催化剂组成直接相关。以固体酸WO3/TiO2为载体,采用浸渍法制备出一系列负载Li、Mn活性组分的催化剂。利用电感耦合等离子体发射光谱(ICP-OES)、X射线衍射(XRD)、高分辨透射电镜(HRTEM)、CO2程序升温脱附(CO2-TPD)、O2程序升温脱附(O2-TPD)、H2程序升温还原(H2-TPR)、拉曼光谱(Raman)、X射线光电子能谱(XPS)和CH4程序升温表面反应(CH4-TPSR)等表征技术对催化剂进行了研究,发现Li的添加提高了C2选择性,并有效抑制了甲烷深度氧化形成CO2的过程。XRD分析表明Li的添加不仅能够促进锐钛矿型二氧化钛向金红石型二氧化钛转化而且促使了高价锰离子的还原。XPS与CO2-TPD分析表明Li的增加有利于增加催化剂表面的晶格氧含量和降低催化剂表面的碱性。O2-TPD分析表明Li含量逐渐升高能够促使晶格氧的移动性增强,从而提高催化剂的反应性能。催化剂的性能受Mn物种的含量与价态的影响,过多的Mn物种对甲烷氧化偶联是不利的,易造成甲烷的深度氧化。同时,Li和Mn活性组分通过协同作用影响着催化剂的反应性能,能够形成新的活性物种MnTiO3提高甲烷氧化偶联的低温活性。催化剂在n(Li) : n(Mn) = 2 : 1、反应温度750 ℃条件下,C2产率达16.3%,表现出最佳催化效果。

关键词: 甲烷氧化偶联, 锰物种, WO3/TiO2, 晶格氧, MnTiO3

Abstract:

The selective oxidation of methane to basic petrochemicals (ethylene and ethane) is desirable and has attracted extensive research attention. The oxidative coupling of methane (OCM) is considered a promising one-step route for the production of C2 compounds (ethylene and ethane) from methane, and has been the focus of industrial and fundamental studies. It is widely accepted that the composition is a crucial factor governing the activity of a catalyst system. It was found that the phase structures, basicity, existing status and distribution of the active components, oxygen species, and chemical states of the catalyst were influenced by the composition and ratio, resulting in different catalytic performances for the OCM. In this study, a series of solid acid WO3/TiO2-supported lithium-manganese oxide catalysts for OCM were synthesized via the impregnation method. The impacts of diverse compositions, such as the individual contents (Li and Mn) and dual contents (Li-Mn), on the OCM were investigated in detail, using inductively coupled plasma optical emission spectrometry, X-ray diffraction, high-resolution transmission electron microscopy, CO2-temperature-programmed desorption, O2-temperature-programmed desorption, H2-temperature-programmed reduction, Raman spectroscopy, X-ray photoelectron spectroscopy, and CH4-temperature-programmed surface reaction. The addition of Li content to the catalyst not only led to the anatase-to-rutile crystal structure transformation of TiO2, and the reduction of the high-valence-state Mn species to low-valence-state Mn, but also increased the content of surface lattice oxygen and decreased the surface basicity. The observed effects on the structures and catalytic performance suggest that the Li content is helpful in suppressing the formation of completely oxidized CO2, and increases the C2 selectivity. Moreover, increasing the Li content of the catalyst facilitated the mobility of the lattice oxygen, which triggered the promotion of CH4 activation, thereby enhancing the OCM catalytic performance. The Mn content acted as the active sites for OCM; therefore, the performance of the catalyst was closely related to the Mn concentration and valence state. However, the WO3/TiO2-supported catalyst with excessive Mn content exhibited a high surface basicity, high valence state of Mn, and low abundant lattice oxygen, which was unfavorable for C2 selectivity. The Raman spectroscopy results revealed that MnTiO3 was formed due to the co-existence of Li and Mn on WO3/TiO2, and played an essential role in improving the low-temperature OCM performance. There was a synergic effect of the Li and Mn components on the OCM. The optimal performance (16.3% C2 yield) was achieved over the WO3/TiO2-supported lithium-manganese catalyst with n(Li) : n(Mn) = 2 : 1 at 750 ℃.

Key words: OCM, Mn species, WO3/TiO2, Lattice oxygen, MnTiO3

MSC2000: 

  • O643