高等学校化学学报 ›› 2024, Vol. 45 ›› Issue (9): 20240125.doi: 10.7503/cjcu20240125

• 物理化学 • 上一篇    下一篇

Pd/LDH低温催化CH4-CO2直接合成乙酸

吴怡枭1, 刘超波2, 昝雪玉1, 张超宇1, 陶诗琪1, 李智雯1, 王柯静1, 刘勇军1(), 黄伟1,3()   

  1. 1.太原理工大学省部共建煤基能源清洁高效利用国家重点实验室, 太原 030024
    2.青岛海西环保科技有限公司, 青岛 266424
    3.山西浙大新材料与化工研究院, 太原 030000
  • 收稿日期:2024-03-18 出版日期:2024-09-10 发布日期:2024-05-31
  • 通讯作者: 刘勇军,黄伟 E-mail:liuyongjun@tyut.edu.cn;huangwei@tyut.edu.cn
  • 作者简介:黄 伟, 男, 博士, 教授, 主要从事煤化工与C1化工方面的研究. E-mail: huangwei@tyut.edu.cn
  • 基金资助:
    国家自然科学基金(21908157);山西浙大新材料与化工研究院研发项目(2021SX-FR009)

Direct Synthesis of Acetic Acid from CH4-CO2 over Pd/LDH at Low Temperature

WU Yixiao1, LIU Chaobo2, ZAN Xueyu1, ZHANG Chaoyu1, TAO Shiqi1, LI Zhiwen1, WANG Kejing1, LIU Yongjun1(), HUANG Wei1,3()   

  1. 1.State Key Laboratory of Clean and Efficient Coal Utilization,Taiyuan University of Technology,Taiyuan 030024,China
    2.Qingdao Haixi Environmental Protection Technology Co. ,Ltd. ,Qingdao 266424,China
    3.Shanxi?Zheda Institute of Advanced Materials and Chemical Engineering,Taiyuan 030000,China
  • Received:2024-03-18 Online:2024-09-10 Published:2024-05-31
  • Contact: LIU Yongjun, HUANG Wei E-mail:liuyongjun@tyut.edu.cn;huangwei@tyut.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21908157);the Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering, China(2021SX-FR009┫.)

摘要:

利用CH4和CO2反应直接合成乙酸是一个100%原子经济同时转化CH4并减排CO2的有效方法. 水滑石因具有比表面积大、 热稳定性高、 活性组分分散性好及适宜的酸-碱性被广泛用于CH4和CO2转化反应中, 而Pd常被认为是C—C键偶联的活性中心. 本文以Mg/Al摩尔比分别为1.5, 3, 5, 7, 9的镁铝水滑石(MgAl-LDH)为载体, 采用离子交换法制备了Pd负载量(质量分数)为5%的Pd/LDH催化剂, 并用于CH4-CO2两步梯阶转化直接合成乙酸; 通过XRD, ICP, 氮气吸附-脱附, XPS, NH3-TPD, CO2-TPD和in situ DRIFTS等表征方法对催化剂的结构和表面酸碱性进行了分析. 结果表明, 由Mg/Al摩尔比为5的LDH载体制备的MA5催化剂乙酸收率最高(61.8 μmol·gcat-1·h-1), 且液相产物只有乙酸; 其收率与催化剂中强酸量和表面Pd0/(Pd2++Pd0)比呈正相关. 催化剂的快速失活源于水滑石结构的坍塌, 进而引起催化剂表面中强酸量大幅减少. 原位红外漫反射光谱结果显示, CH4在Pd/LDH催化剂表面解离生成CH x*中间体和H质子, CO2直接插入CH x*形成CH x COO*, 之后进一步加氢生成乙酸, 或CO2与H质子结合生成COOH*中间体, 之后与CH x*发生偶联形成CH x COOH*, 最后再加氢得到乙酸.

关键词: 甲烷, 二氧化碳, 镁铝水滑石, 钯, 乙酸

Abstract:

The direct synthesis of acetic acid from CH4 and CO2 is an effective method for converting CH4 and reducing CO2 emissions in a 100% atom economy reaction. Hydrotalcite is widely used in CH4 and CO2 conversion reactions due to their large specific surface area, high thermal stability, good dispersion of active metals, and suitable acid-base properties, while Pd is often considered as the active center for C—C bond coupling. Herein, a series of Pd/LDH catalyst with Pd loading of 5%(mass fraction) was prepared by ion-exchange method using magnesium-aluminum hydrotalcite(MgAl-LDH) with Mg/Al molar ratios of 1.5, 3, 5, 7 and 9 as the carrier, and applied for the direct synthesis of acetic acid from CH4-CO2 by a two step-wise technique. The structure and surface acidity-alkalinity of the catalyst were analyzed by XRD, ICP, N2 adsorption-desorption, XPS, NH3-TPD, CO2-TPD and in situ DRIFTS. The results showed that the yield of acetic acid over MA5 catalyst with Mg/Al molar ratio of 5 was the highest(61.8 μmol·gcat-1·h-1), and acetic acid was the only product in the liquid phase product. Its yield was positively correlated with the amount of medium strong acid and surface Pd0/(Pd2++Pd0) ratios. The rapid inactivation of the catalyst was due to the collapse of the hydrotalcite structure, which resulted in a significant decrease in the amount of medium strong acid. In situ DRIFTS experiments showed that CH4 was firstly dissociated to form CH x* intermediate and H proton on the catalyst surface, then CO2 was directly inserted into CHx* to form CH x COO*, with further hydrogenated to yield acetic acid, or CO2 was combined with H protons to form COOH* intermediates which were then coupled with CH x* to form CH x COOH*, and finally hydrogenated to obtain acetic acid.

Key words: Methane, Carbon dioxide, Magnesium-aluminum hydrotalcite, Pd, Acetic acid

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