Formation of defect site on ZIF-7 and its effect on the methoxycarbonylation of aniline with dimethyl carbonate
- Formation of defect site on ZIF-7 and its effect on the methoxycarbonylation of aniline with dimethyl carbonate
- 이현주; 하정명; 이웅; 서보라; 델리아나; 정석현
- Issue Date
- Journal of catalysis
- VOL 380-306
- The Zeolitic Imidazole Framework ZIF-7, (Zn(benzimidazole)2), is known to exhibit a unique gate-opening property depending on the temperature and pressure in the presence of guest molecules, making it useful for H2, CO2, and paraffine separation technology. Besides this distinctive gas adsorption property, ZIF-7 can be used as a catalyst because it contains a Lewis acid site on Zn, and a Lewis basic site on the benzimidazole. In this study, for the first time, we demonstrate that ZIF-7 is a very promising material as a catalyst for the methoxycarbonylation of aniline with dimethyl carbonate (DMC) to produce methyl phenyl carbamate (MPC), an isocyanate precursor. Fresh ZIF-7 showed a high aniline conversion of over 95% at 190？°C for 2？h, and the yield MPC was 60？70% due to the formation of methylated side products, such as N-methyl aniline and N,N′-dimethylaniline. However, interestingly, when the ZIF-7 was reused, the yield of MPC gradually increased and reached over 94.7% by the catalyst’s 6th run. SEM and TEM images revealed the crystalline structure of ZIF-7 collapsed during the reaction due to the leaching of benzimidazole from the ZIF-7, which created defect sites on the Lewis acidic zinc center. Based on 1H NMR and XPS studies, it can be assumed that the DMC binds to the Zn defect sites on the ZIF-7, activating the carbonyl groups on DMC, resulting in the increased selectivity to methoxycarbonylation compared to methylation. Pretreating ZIF-7 with DMC at 190？°C for 6？h could directly activated the ZIF-7 for this methoxycarbonylation reaction. The activated ZIF-7 showed 91.0% MPC yield and the catalyst was reusable.
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