含骨架铁ZSM-5的合成及其负载Pt催化剂在正十二烷脱氢反应中的催化性能

采用水热合成法使铁进入分子筛MFI骨架结构,成功合成出含骨架铁的分子筛Na-Fe]-ZSM-5,并通过离子交换法负载Pt制备脱氢催化剂Pt/Na-Fe]-ZSM-5。通过正十二烷脱氢反应,研究了该催化剂对长链烷烃脱氢制单烯烃反应的催化性能。采用N2吸附-脱附测试、X射线衍射(XRD)、傅立叶变换红外光谱(FT-IR)、氨气程序升温脱附(NH3-TPD)、吡啶吸附的红外光谱(Py-IR)、CO化学吸附、透射电子显微镜(TEM)等不同方法对催化剂进行了表征。结果表明,通过控制骨架铁含量可调控催化剂表面酸性;含骨架铁的ZSM-5分子筛载体具有抑制负载金属晶粒长大,保持金属高分散度的作用;其负载铂催化剂Pt/Na-Fe]ZSM-5-50具有表面弱酸中心(0.69 mmol·g^-1)和高分散Pt中心,因而具有良好的长链烷烃脱氢活性、稳定性和单烯烃选择;在转化率稳定在~20%时,TOF为4.56 s^-1,单烯烃选择性为92.7%;在实验范围内,Pt/Na-Fe]ZSM-5催化剂表面弱酸量和脱氢反应的本征活性(TOF)均随催化剂铁含量的增加而增加。

Synthesis of ZSM-5 Containing Framework Iron and Catalytic Performance of Supported Pt Catalysts in Dehydrogenation of n-Dodecane

The zeolite Na-Fe]-ZSM-5 containing framework iron was successfully synthesized by hydrothermal synthesis, and the Pt/Na-Fe]-ZSM-5 catalysts were prepared by ion exchange method. The catalytic performance of the catalysts for the dehydrogenation of long-chain alkanes to mono-olefin was investigated through the dehydrogenation of n-dodecane. The catalysts were characterized by N₂ adsorption-desorption test, X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), NH₃ temperature-programmed desorption (NH₃-TPD), Ir spectra of pyridine adsorped (Py-IR), CO chemisorption and transmission electron microscope (TEM). The results show that the surface acidity of the catalyst can be adjusted by controlling the content of framework iron; the support, ZSM-5 containing framework iron, has the effect of inhibiting metal grain growth and maintaining high dispersion of metals; The Pt/Na-Fe]-ZSM-5-50 catalyst had weak surface acid sites (0.69 mmol·g^-1) and highly dispersed Pt sites, so it exhibited high activity and stability for the dehydrogenation and high selectivity of mono-olefin. When the conversion was stable at ~20%, the TOF was 4.56 s^-1 and the selectivity of mono-olefin was 92.7%. In the experimental range, the amount of weak acid sites on the surface of Pt/Na-Fe]-ZSM-5 catalyst and its intrinsic activity (TOF) of dehydrogenation increased with the increase of iron content.