催化学报 ›› 2019, Vol. 40 ›› Issue (4): 553-566.DOI: 10.1016/S1872-2067(19)63291-2

• 论文 • 上一篇    下一篇

金属有机框架MOF-808-X高效催化CO2和甲醇直接合成碳酸二甲酯

宣铿a,b, 蒲彦锋a, 李枫a, 雒京a,b, 赵宁a, 肖福魁a   

  1. a 中国科学院山西煤炭化学研究所煤转化国家重点实验室, 山西太原 030001;
    b 中国科学院大学, 北京 100049
  • 收稿日期:2018-11-08 修回日期:2018-12-26 出版日期:2019-04-18 发布日期:2019-03-14
  • 通讯作者: 赵宁, 肖福魁
  • 基金资助:

    山西省自然科学基金(201601D102006);山西省青年科学基金(201701D221052);国家自然科学基金(21776294);山西省重点科技攻关项目(MD2014-09,MD2014-10);煤转化国家重点实验室自主研究课题(2018BWZ002).

Metal-organic frameworks MOF-808-X as highly efficient catalysts for direct synthesis of dimethyl carbonate from CO2 and methanol

Keng Xuana,b, Yanfeng Pua, Feng Lia, Jing Luoa,b, Ning Zhaoa, Fukui Xiaoa   

  1. a State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, Shanxi, China;
    b University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2018-11-08 Revised:2018-12-26 Online:2019-04-18 Published:2019-03-14
  • Supported by:

    This work was financially supported by the Natural Science Foundation of Shanxi Province, China (201601D102006), the Science Foundation for Young Scientists of Shanxi Province, China (201701D221052), the National Natural Science Foundation of China (21776294), the Key Science and Technology Program of Shanxi Province, China (MD2014-09, MD2014-10), and the Independent Research Project of the State Key Laboratory of Coal Conversion (2018BWZ002).

摘要:

碳酸二甲酯(DMC)是一种重要的绿色无毒化工原料,其分子结构中含有甲基、甲氧基和羰基等官能团.DMC既可以替代卤代甲烷和硫酸二甲酯用作甲基化试剂,替代剧毒的光气用作羰基化试剂,也可以与醇类、酯类及氨基醇类进行酯交换反应用于合成树脂和精细化学品.此外,DMC因具有相容性好、含氧量高和饱和蒸气压低等特点,还可用作低毒溶剂和燃油添加剂.目前,已报道的DMC合成方法主要包括光气法、甲醇氧化羰基化法、酯交换法、尿素醇解法和直接合成法.其中,以CO2和甲醇为原料直接合成DMC的方法受到广泛关注.该方法不仅具有原料价格低廉、工艺简单、原子经济性高的优点,还可以将温室气体CO2资源化利用,有望成为未来生产DMC的一条全新的高效途径.目前,用于该反应的催化剂研究主要集中在金属氧化物和改性金属氧化物上,这些催化剂存在比表面积较小、活性位点数量不足以及活性不高的缺点.
本文针对传统金属氧化物的缺点,合成了一系列锆基金属有机框架催化剂MOF-808-X(X为ZrOCl2·8H2O/均苯三甲酸(BTC)的摩尔比),并将其用于催化CO2和甲醇合成DMC,系统考察了MOF-808-X合成过程中ZrOCl2·8H2O/BTC摩尔比对MOF-808-X催化剂组成、比表面积、孔道结构以及酸碱位点数量的影响,探讨了MOF-808-X催化剂物化性质与其催化性能之间的关系.结果表明,通过调控ZrOCl2·8H2O/BTC摩尔比,可以减少堵塞在MOF-808-X微孔中未反应的配体BTC或氧化锆原子簇的量,提高MOF-808-X的比表面积、微孔孔径以及酸碱位点数量,从而显著提升MOF-808-X催化剂的催化活性.当ZrOCl2·8H2O/BTC摩尔比=4时,MOF-808-4催化剂具有最大的比表面积、最大的微孔孔径和最多的酸碱性位点,因而表现出最高的催化活性.与我们之前报道的UiO-6-24相比,虽然MOF-808-4的比表面积和酸碱位点数更小,但由于MOF-808-4具有更大的微孔孔径(1.8 nm),其微孔内的活性位点具有更高的催化效率,MOF-808-4表现出了更高的催化活性.原位红外光谱结果表明,酸性位点活化甲醇生成甲基阳离子的过程是该反应的速率控制步骤,由于MOF-808-4中Zr6原子簇上酸碱位点相互邻近,吸附在相邻碱性位点上的中间产物羰基甲氧基可以与酸性位点上的甲基阳离子迅速反应,促进甲基阳离子和DMC的生成,从而进一步提高MOF-808-4的催化活性.此外,催化剂重复利用实验结果表明,MOF-808-X催化剂结晶度越好,催化剂重复利用性能越好.MOF-808-X催化剂在CO2和甲醇直接合成DMC反应中的成功应用可为开发用于该反应的高效非均相催化剂提供新的思路.

关键词: 金属有机框架, MOF-808, 微孔孔径, 二氧化碳, 甲醇, 碳酸二甲酯

Abstract:

A series of metal-organic frameworks MOF-808-X (6-connected) were synthesized by regulating the ZrOCl2·8H2O/1,3,5-benzenetricarboxylic acid (BTC) molar ratio (X) and tested for the direct synthesis of dimethyl carbonate (DMC) from CO2 and CH3OH with 1,1,1-trimethoxymethane (TMM) as a dehydrating agent. The effect of the ZrOCl2·8H2O/BTC molar ratio on the physicochemical properties and catalytic performance of MOF-808-X was investigated. Results showed that a proper ZrOCl2·8H2O/BTC molar ratio during MOF-808-X synthesis was fairly important to reduce the redundant BTC or zirconium clusters trapped in the micropores of MOF-808-X. MOF-808-4, with almost no redundant BTC or zirconium clusters trapped in the micropores, exhibited the largest surface area, micropore size, and the number of acidic-basic sites, and consequently showed the best activity among all MOF-808-X, with the highest DMC yield of 21.5% under the optimal reaction conditions. Moreover, benefiting from the larger micropore size, MOF-808-4 outperformed our previously reported UiO-66-24 (12-connected), which had even more acidic-basic sites and larger surface area than MOF-808-4, mainly because the larger micropore size of MOF-808-4 provided higher accessibility for the reactant to the active sites located in the micropores. Furthermore, a possible reaction mechanism over MOF-808-4 was proposed based on the in situ FT-IR results. The effects of different reaction parameters on DMC formation and the reusability of MOF-808-X were also studied.

Key words: Metal-organic frameworks, MOF-808, Micropore size, Carbon dioxide utilization, Dimethyl carbonate