介孔磷酸铌一锅法高效催化木糖制备糠醛

One-Pot Catalytic Conversion of Xylose to Furfural on Mesoporous Niobium Phosphate

木糖转化到糠醛一般包括两步:首先在酶、碱或路易斯(L)酸的催化作用下异构化木糖到木酮糖,接下来木酮糖在酸的作用下脱水得到糠醛.针对木糖水相脱水一步制备糠醛,利用十六烷基三甲基溴化铵(CTAB)为模板剂,借助软模板合作策略制备了一种抗水的新型固体酸催化剂,介孔磷酸铌,并利用X射线衍射(XRD)、N2吸脱附、透射电镜(TEM)、氨气程序升温脱附(NH3-TPD)和吡啶吸附傅里叶变换红外(Py-FTIR)光谱对材料的结构和酸性质进行了表征.研究发现介孔磷酸铌不仅具有很高的比表面积(>200m2·g-1),比较窄的孔径分布(3.5nm),同时还具有很强的L酸性和布朗斯特(B)酸性.通过L酸催化的木糖异构化为木酮糖/来苏糖和B酸催化的木酮糖/来苏糖进一步脱水得到糠醛,实现了一步由木糖到糠醛的高效转化.为了优化反应条件,考察了水溶液中反应温度、投料质量比及反应时间对木糖转化率和糠醛收率的影响,在最佳的反应条件下,木糖的转化率为96.5%,糠醛的收率达49.8%.进一步地,为了提高收率且易于分离,利用4-甲基-2-戊酮(MIBK)/NaCl水溶液(体积比为7:3)作为反应混合溶剂,使糠醛收率提高到68.4%.

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 （3.5nm）,but also had relatively strong Lewis and Bro/nsted 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.