纳米片型MFI分子筛催化裂解正己烷性能研究

Study on Catalytic Performance of Nanosheet MFI Structured Zeolite in n-Hexane Cracking

针对传统的ZSM-5仅具有微孔结构、扩散路径长、易失活等缺陷,合成了纳米片型MFI分子筛(MFI-Al),并进行了X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、NH_3程序升温脱附(NH_3-TPD)、吡啶吸附红外和N_2吸附-脱附表征。与传统的ZSM-5相比,MFI-Al具有更高的比表面积(479m2/g)、更多的介孔结构、超薄的片层结构以及更大的孔容(1.05cm3/g)。利用固定床反应器,将其应用于催化裂解正己烷来评价其催化活性,并与ZSM-5进行对比。结果表明:MFI-Al具有更好的催化活性。MFI-Al催化正己烷的转化率在720min后依然保持在80%左右,远高于ZSM-5催化的转化率(40%)。MFI-Al的丙烯选择性也高于ZSM-5。MFI-Al的积碳量仅为50.1mg/(g cat),低于ZSM-5的积碳量(117.3mg/(g cat))。因此,MFI-Al因其特殊的形貌结构以及适量的酸性,增加了分子扩散效率和酸性位点的可接触性,使其具有更高的催化性能。

In order to overcome the disadvantages of single microporous,long diffusion length and easy deactivation of the conventional ZSM-5 zeolite,nanosheet MFI typed zeolite(MFI-Al)was successfully prepared and characterized by X ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM),NH 3 temperature-programmed desorption(NH 3-TPD),pyridine-absorbed FT-IR and N 2 adsorption-desorption.MFI-Al zeolite has high BET surface area(479 m 2/g),large mesopores,ultrathin lamellar structure and large pore volume(1.05 cm 3/g).It shows promising catalytic activity in n-hexane cracking,which was carried out in a fixed bed reactor and compared with that of conventional ZSM-5 zeolite.Catalytic results indicate that MFI-Al zeolite shows much higher catalytic activity and stability.The cracking conversion of n-hexane over MFI-Al zeolite is about 80%even after reaction time over 720 min,which is much higher than that of ZSM-5 zeolite(about 40%).The selectivity of propylene over MFI-Al zeolite is also higher than that of the conventional ZSM-5 zeolite.The carbon deposition on MFI-Al zeolite is 50.1 mg/(g cat),which is far less than that on ZSM-5 zeolite(117.3 mg/(g cat)).Consequently,the excellent catalytic performance is attributed to the superior morphology and suitable acid properties of nanosheet MFI zeolite.