关键词: 介孔磷酸铌, 布朗斯特酸, 路易斯酸, 木糖, 糠醛, 水相, 双相

Abstract:

The conversion of xylose to furfural normally involves two steps: the isomerization of xylose to xylulose catalyzed by an enzyme, a base or a Lewis acid, followed by the acid-catalyzed dehydration of xylulose to furfural. To allow a more efficient single-step conversion, a new water-tolerant solid acid catalyst, mesoporous niobium phosphate was synthesized. This synthesis was performed using a soft template approach, with cetyltriethylammonium bromide (CTAB) as the template. The structure and properties of the catalyst thus synthesized were investigated by X-ray diffraction (XRD), N₂ sorption, transmission electron microscopy (TEM), temperature-programmed desorption of NH₃ (NH₃-TPD), and pyridine sorption FTIR (Py-FTIR). These studies determined that the niobium phosphate not only had a large surface area (>200 m²·g^-1) and narrow pore size distribution (3.5 nm), but also had relatively strong Lewis and Brønsted acidity. This catalyst was found to be capable of producing furfural via a simple one-pot process, including the isomerization of xylose to xylulose and subsequent dehydration. The influence of several variables including temperature, mass ratio of xylose/catalyst, and reaction time on the extent of xylose conversion and furfural yield were studied. Under optimal conditions, the yield of furfural in aqueous solution reached 49.8% with 96.5% xylose conversion. It was further determined that both the yield and the separation of furfural could be improved by employing a methyl isobutyl ketone (MIBK)/water (volume ratio 7:3) biphase containing NaCl in the aqueous phase, resulting in a 68.4% yield.

Key words: Mesoporous niobium phosphate, Brö, nsted acid, Lewis acid, Xylose, Furfural, Aqueous phase, Biphase