合成類沸石咪唑骨架材料(ZIF-8)衍生之摻氮多孔碳材並應用於糠醛至馬來酸之轉化

Abstract

馬來酸 (maleic acid; MA) 和馬來酸酐 (maleic anhydride) 為重要的四碳化合物，常被用於生產高附加值的化學品。然而在傳統工業中，馬來酸酐的生產是透過石油化學途徑，藉由氧化正丁烷和苯等可耗盡且不可再生的原料製備而成。反之，自生物質轉換所得之可再生資源，糠醛，也可經由氧化催化反應製備馬來酸。過去有關於糠醛製備馬來酸的轉化，大多以酸性催化爲主並存在許多的缺點。因此，本研究使用衍生自ZIF-8 的摻氮多孔碳材 (NC)，首次在非酸性的環境中，將糠醛氧化轉化成馬來酸。ZIF-8 是一種典型的類沸石咪唑骨架材料 (ZIF)，可作爲自體模板，進一步鍛燒加以碳化得到摻氮之多孔碳材。本研究將ZIF-8 於不同溫度下進行碳化， 以探討碳化溫度對碳材之氮原子組態的影響。我們也研究了各種反應參數，包含溶劑，雙氧水濃度，反應溫度和時間對MA產率的影響。透過NC-900催化劑，雙氧水 (35 wt%)作為氧化劑，在80 °C 下，我們可在5 小時內達成最高61% 之馬來酸產率。我們推測此反應之路徑是透過氧化開環，形成5-羥基-2(5H)-呋喃酮 (5-hydroxy-furan-2(5H)-one)作為主要中間產物，隨後進行Baeyer-Villiger 氧化，重排步驟和水解，進而得到馬來酸 。

Maleic acid (MA) and maleic anhydride are important C4 chemical intermediates to produce high value-added chemicals. In industry, maleic anhydride is commercially produced through petrochemical route by the oxidation of the exhaustible and non-renewable feedstocks, n-butane and benzene. On the other hand, the renewable resource, furfural derived from lignocellulosic biomass, has been recognized as a potential bio-based platform chemical to produce MA through catalytic oxidation. Until now, the conversion of furfural to MA has been mainly catalyzed by an acidic catalyst, which exhibited several drawbacks. Here, we report the first acid-free system for furfural to MA conversion, by using the nitrogen-doped nanoporous carbon material (NC) derived from zeolitic imidazolate frameworks (ZIF-8). The synthesized ZIF-8 was undergoing direct carbonization at different temperatures in order to investigate the effect of carbonization temperature on nitrogen configuration in the resulted carbon materials. The effect of reaction parameters, including H2O2 concentration, solvent, reaction temperature and time were systematically studied. A MA yield as high as 61 % was achieved over NC-900 catalyst at 80 °C in 5 hours, assisted by 35 wt% H2O2. The kinetics study indicates that the mechanism was via the oxidative ringopening reaction and formation 5-hydroxy-furan-2(5H)-one as the main intermediate, following by Baeyer-Villiger oxidation, rearrangement steps, and hydrolysis to form MA.