PdZn合金催化剂调控CO酯化产物选择性: 从草酸二甲酯到碳酸二甲酯

doi:10.6023/A24110346

摘要/Abstract

目前, 中国已建成千万吨级煤制乙二醇生产装置, 由于乙二醇市场行情不好, 导致很多生产装置处于停产状态, 迫切需要转型. 煤制乙二醇中CO酯化可以生产草酸二甲酯(DMO)和碳酸二甲酯(DMC)两种重要的酯类化学品. 把产物DMO转变为附加值更高的DMC是一条转型思路. DMO可通过脱羰反应变成DMC, 但需要增加新的反应器和催化剂. 如果利用煤制乙二醇的旧装置, 通过更换新型催化剂, 直接产出DMC, 更具有经济性, 也更具有挑战. Pd/α-Al₂O₃是传统的DMO生产催化剂. 本工作提出了PdZn合金化策略, 调控CO酯化产物选择性, 实现了产物选择性从DMO调变为DMC. 相比Pd/α-Al₂O₃, PdZn(1:4)/α-Al₂O₃的DMO选择性显著下降(85.8%→16.8%), 而DMC选择性显著上升(14.2%→83.2%). 通过透射电子显微镜(TEM)和X-射线光电子能谱(XPS)等表征手段, 证明形成了PdZn合金, 且Zn降低了Pd的电子密度, 使部分Pd处于单位点的Pd^δ⁺状态, 从而高选择性生成DMC. 本工作为煤制乙二醇装置DMO改产DMC提供了一种新思路.

关键词: PdZn合金, 电子转移, 碳酸二甲酯, CO酯化反应

Currently, 10 million tons of coal to ethylene glycol (CTEG) plants have been built in China. Due to the poor market conditions of ethylene glycol, many plants are in a state of shutdown and are in urgent need of transformation. CO esterification in CTEG can produce two important ester chemicals, dimethyl oxalate (DMO) and dimethyl carbonate (DMC). Converting the product DMO into higher value-added DMC is one of the transition ideas. DMO can be converted to DMC by decarbonylation, but new reactors and catalysts are needed. It would be more economical and challenging to utilize CTEG plant to produce DMC directly by replacing the catalyst with a new one. Pd/α-Al₂O₃ is the traditional catalyst for DMO production. In this work, we proposed a PdZn alloying strategy to modulate the selectivity of CO esterification products, and realize the product selectivity change from DMO to DMC. Compared with Pd/α-Al₂O₃, the selectivity to DMO over PdZn(1:4)/α-Al₂O₃ was significantly decreased (85.8%→16.8%), and the DMC selectivity was increased remarkably (14.2%→83.2%). The formation of PdZn alloy was demonstrated by X-ray diffraction (XRD), transmission electron microscope (TEM), and other characterizations, X-ray photoelectron spectroscopy (XPS) results showed that the alloy formed between Zn and Pd significantly changed the electron density of the Pd component, and the Pd component was in an electron-deficient state, which was conducive to the improvement of the performance of the DMC reaction. In addition, the results of CO diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization showed that Zn can disperse Pd. With the increase of the second metal Zn content, the continuous Pd metal phase disappears, and an isolated single-atom alloy state may be formed, which inhibits the formation of the byproduct DMO. The present study not only provides a new way to regulate the selectivity of CO esterification products, but also provides an idea for the conversion of CTEG plants.

Key words: PdZn alloy, electron transfer, dimethyl carbonate, CO esterification reaction

引用此文

李翔宇, 李家凯, 林淑娟, 王明盛, 孙径, 徐忠宁, 郭国聪. PdZn合金催化剂调控CO酯化产物选择性: 从草酸二甲酯到碳酸二甲酯[J]. 化学学报, 2025, 83(3): 206-211.

Xiang-Yu Li, Jia-Kai Li, Shu-Juan Lin, Ming-Sheng Wang, Jing Sun, Zhong-Ning Xu, Guo-Cong Guo. PdZn Alloy Catalysts Modulating the Selectivity of CO Esterification Products: from Dimethyl Oxalate to Dimethyl Carbonate[J]. Acta Chimica Sinica, 2025, 83(3): 206-211.

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图/表 7

图1. 不同催化剂在CO酯化反应中的产物选择性. 基于反应物CO来计算产物选择性, 不考虑反应中亚硝酸甲酯(MN)的分解带来的影响. 反应条件: 200 mg催化剂, 120 ℃, 0.1 MPa, WHSV=2500 L?kgcat.?1?h?1, CO/MN/Ar/N2流量比19∶45∶3∶33

Figure 1. Product selectivity in CO esterification reaction of different catalysts. The selectivities were calculated based on CO, without considering the decomposition of MN. Reaction conditions: 200 mg catalyst, 120 ℃, 0.1 MPa, weight hour space velocity (WHSV)=2500 L?kgcat.?1?h?1, flow ratio of CO/MN/Ar/N2 is 19∶45∶3∶33

催化剂	Pd负载量^a/%	Zn负载量^a/%^a	分散度^b/%	CO转化率/%	DMC选择性/%
Pd	0.97	—	9.32	68.4	14.2
PdZn(1:1)	1.00	0.96	13.98	83.9	35.9
PdZn(1:2)	0.98	2.08	16.37	84.5	41.0
PdZn(1:4)	0.96	3.83	23.68	88.4	83.2

表1. 催化反应性能、负载量及分散度

Table 1. Catalytic performance, metal loading and metal dispersion

图2. (a) Pd/α-Al2O3, PdZn(1:1)/α-Al2O3, PdZn(1:2)/α-Al2O3和Pd-Zn(1:4)/α-Al2O3的XRD谱图; 底部的棕色竖条表示α-Al2O3相的标准数据(PDF#50-1496); (b) 以上催化剂(2θ=39°~43°)部分放大的XRD谱图

Figure 2. (a) XRD patterns of Pd/α-Al2O3, PdZn(1:1)/α-Al2O3, PdZn(1:2)/α-Al2O3 and PdZn(1:4)/α-Al2O3. Brown vertical bars at the bottom denote the standard data for α-Al2O3 phase (PDF#50-1496); (b) partially zooming XRD spectra from 2θ=39°~43° of the above catalysts

图3. Pd/α-Al2O3, PdZn(1:1)/α-Al2O3, PdZn(1:2)/α-Al2O3和PdZn(1:4)/ α-Al2O3催化剂的H2-TPR图

Figure 3. H2-TPR profiles of calcined Pd/α-Al2O3, PdZn(1:1)/α-Al2O3, PdZn(1:2)/α-Al2O3 and PdZn(1:4)/α-Al2O3 catalysts

图4. (a) PdZn(1:4)/α-Al2O3催化剂的TEM图和(b) HRTEM图像; (c) PdZn(1:4)/α-Al2O3催化剂的HAADF-STEM图像; (d~h)与之对应的Al、O、Pd、Zn和Pd、Zn元素混合的EDX mapping图像

Figure 4. (a) TEM and (b) HRTEM images of PdZn(1:4)/α-Al2O3 catalyst; (c) HAADF-STEM image of PdZn(1:4)/α-Al2O3; (d~h) the corresponding elemental mapping of Al, O, Pd, Zn and Pd, Zn mixing

图5. Pd/α-Al2O3, PdZn(1:1)/α-Al2O3, PdZn(1:2)/α-Al2O3和PdZn(1:4)/ α-Al2O3样品的XPS谱图

Figure 5. XPS spectra of Pd/α-Al2O3, PdZn(1:1)/α-Al2O3, PdZn(1:2)/ α-Al2O3 and PdZn(1:4)/α-Al2O3 samples

图6. Pd/α-Al2O3, PdZn(1:1)/α-Al2O3, PdZn(1:2)/α-Al2O3, PdZn(1:4)/ α-Al2O3和Zn/α-Al2O3样品上的CO原位漫反射傅里叶变换红外光谱

Figure 6. In situ CO-DRIFTS of Pd/α-Al2O3, PdZn(1:1)/α-Al2O3, PdZn(1:2)/α-Al2O3, PdZn(1:4)/α-Al2O3 and Zn/α-Al2O3 samples

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