干胶法合成Sn-Beta沸石及其糠醛转化性能

Preparation and Properties of Sn-Beta Zeolite via Dry Gel Conversion Method for Furfural Conversion

报道了一种无氟体系下利用干胶法合成的具有BEA拓扑结构的含Sn的Beta沸石(Sn-Beta沸石)的方法,并将其用于糠醛选择性转化成醇和酯的反应。采用FT-IR、吡啶红外、XRD、XRF、SEM和氮气吸附研究了Sn-Beta沸石的物性。结果表明:在相同投料Si/Sn比(Si/Sn=160)条件下,水热法制得沸石结晶度仅为干胶法制得沸石的40%,且干胶法所得沸石Si/Sn比为152,较水热法所得沸石Si/Sn比(176)低。在糠醛转化反应中,干胶法所得Sn-Beta沸石的转换频率(TOF值)为7.3 h-1,优于水热法合成的沸石(3.4 h-1)。通过对比Sn-Beta沸石(骨架含Sn和Si)、Sn-Al-Beta沸石(骨架含Sn、Al和Si)和Beta沸石(骨架含Si和Al)催化糠醛转化反应发现,干胶法合成的Sn-Beta沸石活性位主要以Lewis酸(L酸)为主,L酸和Br nsted酸(B酸)数量的比值(L/B)为14.5,在糠醛转化反应中发生Meerwein-Ponndorf-Verley(MPV)还原反应将糠醛转化为糠醇;Beta沸石活性位为B酸和L酸,L/B比值为1.1,能直接将糠醛催化转化成当归内酯,且通过Sn的引入合成Sn-Al-Beta沸石,L/B比值提高到2.4,糠醛转化TOF值由4.2 h-1提高至5.4 h-1。

Here,we reported a synthetic strategy for the synthesis of Sn-Beta zeolite with BEA topology structure and framework Sn without the use of fluorine compounds during synthesis process.The as-prepared zeolite was used in the selective conversion of furfural to alcohols and esters.The zeolite was characterized by the XRD,XRF,SEM,FT-IR,pyridine-IR and nitrogen sorption,respectively.For the Sn-Beta zeolite synthesized with the same Si/Sn ratio of 160 in raw materials,the zeolite obtained by hydrothermal method shows only 40%relative crystallinity of that obtained by the dry gel conversion method.The Si/Sn ratio of zeolite obtained by the dry gel conversion method is 152,which is lower than that of zeolite obtained by hydrothermal method(176).This indicates that a higher framework Sn content can be achieved by the dry gel conversion method.For the furfural conversion reaction,the turnover frequency(TOF)of Sn-Beta zeolite obtained by dry gel conversion method is 7.3 h-1,which is higher than that from hydrothermal synthesis method(3.4 h-1).The catalytic performance of furfural conversion on Sn-Beta(with framework Sn and Si)zeolite,Sn-Al-Beta(with framework Sn,Al and Si)zeolite and Beta(with framework Si and Al)zeolites was focused.The Sn-Beta zeolite synthesized from dry gel conversion or hydrothermal synthesis method is characteristic of Lewis acid(L acid)sites with a high ratio of L acid site to Br nsted acid(B acid)(L/B)at 14.5,which catalyzes the Meerwein-Ponndorf-Verley(MPV)reduction reaction to convert furfural to furfural alcohols.However,Beta zeolites synthesized by dry gel conversion method possess both B acid and L acid sites,which are mainly B acid sites with strong acid strength and a L/B ratio at 1.1,and they can directly catalyze the conversion of furfural to Angelica lactone.Moreover,the L/B acid site ratio can be adjusted by the introduction of Sn to the Beta zeolite to 2.4,and then enhances the TOF value from 4.2 h-1 to 5.2 h-1.