物理化学学报

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不同结构导向剂合成不同硅含量SAPO-34分子筛的酸性质

王磊1,2, 孙毯毯1,3, 闫娜娜1,3, 刘晓娜1,3, 马超1,3,4, 徐舒涛1, 郭鹏1, 田鹏1, 刘中民1   

  1. 1 中国科学院大连化学物理研究所, 甲醇制烯烃国家工程实验室, 洁净能源国家实验室, 辽宁 大连 116023;
    2 郑州大学化学学院, 河南先进技术研究所, 郑州 450001;
    3 中国科学院大学, 北京 100049;
    4 大连理工大学张大煜学院, 辽宁 大连 116024
  • 收稿日期:2020-03-19 修回日期:2020-05-17 录用日期:2020-05-18 发布日期:2020-05-25
  • 通讯作者: 郭鹏, 刘中民 E-mail:pguo@dicp.ac.cn;zml@dicp.ac.cn
  • 基金资助:
    国家自然科学基金(21972136, 21676262, 21991091), 中国科学院百人计划(Y706071202), 中国科学院洁净能源创新研究院合作基金(DNL201908)及 中国科学院前沿科学重点研究计划(QYZDBSSW-JSC040)资助项目

Acid Properties of SAPO-34 Molecular Sieves with Different Si Contents Templated by Various Organic Structure-Directing Agents

Lei Wang1,2, Tantan Sun1,3, Nana Yan1,3, Xiaona Liu1,3, Chao Ma1,3,4, Shutao Xu1, Peng Guo1, Peng Tian1, Zhongmin Liu1   

  1. 1 National Engineering Laboratory for Methanol to Olefins, Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning Province, P. R. China;
    2 College of chemistry, Henan Institute of Advanced Technology, Zhengzhou University, Zhengzhou 450001, P. R. China;
    3 University of Chinese Academy of Sciences, Beijing 100049, P. R. China;
    4 Zhang Dayu School of Chemistry, Dalian University of Technology, Dalian 116024, Liaoning Province, P. R. China
  • Received:2020-03-19 Revised:2020-05-17 Accepted:2020-05-18 Published:2020-05-25
  • Supported by:
    The project was supported by the National Natural Science Foundation of China (21972136, 21676262, 21991091), the CAS Pioneer Hundred Talents Program (Y706071202), the Dalian National Laboratory for Clean Energy, (DNL) Cooperation Fund, Chinese Academy of Sciences (DNL201908) and the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (QYZDBSSW-JSC040).

摘要: SAPO-34分子筛由于其独特的拓扑结构和适宜的酸性,在以甲醇制烯烃(MTO)和氨气选择性催化还原NOx (NH3-SCR)为代表的系列催化反应中显示了优良的性能,因此吸引了研究者的广泛关注。但是,在合成过程中如何通过选择有机模板和控制硅含量来得到合适酸量的SAPO-34催化剂是极具挑战的。本文中,四个系列的SAPO-34分子筛,即分别由四乙基氢氧化铵(TEAOH)、二异丙胺(DIPA)、正丁胺(nBA)和吗啉(MOR)为有机模板剂合成不同硅含量的样品,通过热重量分析(TG),结构精修和固态核磁进行了研究。TG和结构精修结果显示在TEAOH和DIPA合成的SAPO-34分子筛cha(一种复合结构单元)笼子中只有一个结构导向剂而MOR和nBA合成的SAPO-34分子筛的cha笼中有两个。采用固态核磁氢谱(1H ss-NMR)探究碱性探针分子氘代乙腈(CD3CN)和分子筛骨架之间主客体的相互作用,并对其酸性(酸量和酸强度)进行了系统的研究。例如,TEAOH合成的SAPO-34分子筛随着硅含量的增加酸强度增加而酸量却保持着不变。而DIPA合成的SAPO-34,与前者存在较大的差异,即随着硅含量的上升,酸量显著下降而酸强度只发生了微小的变化。该工作为SAPO-34分子筛催化剂酸性的定向调变提供了理论基础。

关键词: SAPO-34, 有机模板剂, 酸性质, 固体核磁, 结构精修, 硅分布, 多孔材料

Abstract: The acid properties of SAPO-34 molecular sieves (MSs), including the strength and density of Brönsted acids, have attracted enormous attention in past decades because of the excellent performance of SAPO-34 in industrial processes such as the methanol-to-olefins (MTO) process and the selective catalytic reduction of NOx with NH3 (NH3-SCR). Currently, pure-phase SAPO-34 MSs with different Si contents can be easily obtained by utilizing multifarious organic structure-directing agents (OSDAs). However, the resulting SAPO-34 MSs have different acid properties, which may affect their catalytic performance. Hence, correlating the acid properties with the OSDAs and Si contents is of significance to synthesize SAPO-34 MSs with the desired properties. Herein, the acid properties of four series of SAPO-34 MSs with varying Si contents synthesized using tetraethylammonium hydroxide (TEAOH), diisopropylamine (DIPA), n-butylamine (nBA), and morpholine (MOR) as the OSDAs were probed in detail by thermogravimetry (TG), Rietveld refinement, and solid-state nuclear magnetic resonance (ss-NMR) analyses. The strength and acid density were systematically investigated by exploring the host-guest interactions between the probed molecule CD3CN and the framework using 1H magic angle spinning (MAS) NMR spectroscopy, and the local environments of Si were studied by 29Si MAS NMR spectroscopy. The results of TG and Rietveld refinement showed that the SAPO-34 MSs templated by TEAOH and DIPA have only one OSDA per cha (one of the composite building units) cage in the longitudinal configuration, while those templated by nBA and MOR possess two OSDAs occluded in the cha cage in an up-and-down arrangement. Interestingly, the acid strength of SAPO-34 templated by TEAOH increased with increasing Si content, while the acid density remained almost unchanged. In contrast, the acid density of SAPO-34 templated by DIPA decreased evidently with an increase in the Si content, while the acid strength showed only a small variation. Among the other two samples, SAPO-34 templated by MOR has the most amounts of acid densities compared to SAPO-34 templated by nBA, while the strength is not superior. Thus, we conclude that the acid density is associated with the number of OSDAs in each cha cage and their protonation ability, while the difference in acid strength is attributed to the number of Si atoms at the edges of the Si islands. The findings of this study will provide insight into the acid properties of related crystalline porous materials.

Key words: SAPO-34, OSDA, Acid property, ss-NMR, Rietveld refinement, Si distribution, Porous materials

MSC2000: 

  • O641