Chem. J. Chinese Universities ›› 2024, Vol. 45 ›› Issue (9): 20240125.doi: 10.7503/cjcu20240125

• Physical Chemistry • Previous Articles     Next Articles

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┫.)

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

CLC Number: 

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