Enhanced activity and stability over hierarchical porous mordenite (MOR) for carbonylation of dimethyl ether: Influence of mesopores
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摘要: 本研究通过调整聚乙二醇(PEG 1450)的添加量制备了介孔量不同的梯级孔丝光沸石,并分别对其结构和二甲醚羰基化反应性能进行了表征和评价。结果表明,通过提高PEG1450加入量的方式可以提高丝光沸石的介孔量,但PEG 1450的添加量过高时不利于介孔的形成。当引入的介孔量适宜时丝光沸石能够保持原有的结构,强酸中心数量增多、弱酸和中强酸数量降低,二甲醚的传质效率和二甲醚羰化反应催化性能明显提高。受传质过程和酸分布的影响,梯级孔丝光沸石催化剂上二甲醚羰化反应活性明显改善,二甲醚转化率升高、单程寿命延长,重积炭的形成明显受到抑制。PEG1450的最优添加量为丝光沸石合成时凝胶质量的2%。Abstract: The dimethyl ether (DME) carbonylation reaction over mordenite is greatly affected by the mass transfer process. In this research, hierarchical mordenite catalysts were synthesized and characterized to investigate the influence of mesopores on the structure, mass transfer and catalytic performance. The results show that the medium-strong acid sites decrease while strong acid sites increase over the hierarchical samples. The introduced mesopores can significantly improve the mass transfer efficiency and the carbonylation performances are markedly improved on the hierarchical samples. In addition, the polymerization degree of coke deposition on the deactivated samples decreases although the coke amount increases. Excessive usage of mesopore templates can damage the structure of the MOR catalysts, thus leading to the loss of acid sites and the decrease in catalytic performance.
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Key words:
- PEG /
- MOR /
- carbonylation /
- mass transfer /
- coke deposition
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Table 1 Structural properties of the hierarchical MOR samples
Sample SiO2/Al2O3a SBET /(m2·g-1) vMib /(mL·g-1) vMec /(mL·g-1) vTd /(mL·g-1) S-0 17.8 487.1 0.182 0.019 0.201 S-0.5 18.1 490.9 0.179 0.027 0.206 S-1.0 17.7 534.8 0.180 0.029 0.209 S-2.0 17.9 527.4 0.181 0.032 0.213 S-4.0 18.5 505.3 0.174 0.026 0.200 a: determined by XRF; b: volume of micropores; c: volume of mesopores; d: total pore volumes Table 2 Distribution of acid sites over the MOR samples
Sample NH3-TPD/(mmol·g-1) weaka medium-strongb strongc total S-0 0.16 0.46 0.38 1.01 S-0.5 0.16 0.24 0.49 0.89 S-1.0 0.15 0.28 0.52 0.95 S-2.0 0.15 0.25 0.48 0.88 S-4.0 0.07 0.20 0.35 0.62 a: 40-150 ℃; b: 150-270 ℃; c: 270-700 ℃ Table 3 Distribution of acid sites over the MOR samples
Sample Py-FTIR at 150 ℃ Py-FTIR at 300 ℃ OH-IR B acid sites/
(mmol·g-1)L acid sites/
(mmol·g-1)B acid sites/
(mmol·g-1)L acid sites/
(mmol·g-1)B acid in 12 MR1/
(a.u.)B acid in 8 MR2/
(a.u.)S-0 0.53 0.17 0.27 0.03 741 1506 S-0.5 0.44 0.15 0.31 0.02 593 1215 S-1.0 0.46 0.14 0.34 0.02 637 1367 S-2.0 0.42 0.16 0.30 0.03 676 1461 S-4.0 0.35 0.19 0.19 0.03 479 905 1: calculated from the OH-IR peak at 3610 cm-1; 2: calculated from the OH-IR peak at 3590 cm-1 -
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