MOR沸石的骨架原子抽离及其对四氢萘裂解的影响

Effects on Tetralin Catalytic Hydrocracking over Mordenite Zeolites Treated by Framework Atoms Extraction

以铵型MOR沸石为母体,在酸性和碱性介质中进行了骨架硅、骨架铝原子的抽离,利用X射线衍射(XRD)、电耦合高频等离子发射光谱(ICP)、27Al/29Si核磁共振(27Al/29Si NMR)、傅里叶变换红外光谱(FT-IR)、扫描电镜(SEM)、透射电镜(TEM)和氮气吸脱附等方法表征了分子筛的物化性质,并考察了其催化四氢萘裂解反应的性能。结果表明,通过碱或酸处理可有效地将骨架硅和铝原子抽离,可控调变MOR沸石的骨架结构和硅铝比,达到修饰MOR沸石孔道和酸性的目的。在四氢萘催化裂解反应中,样品经碱处理脱硅后引入了介孔,单位酸密度升高,有效提高了稠环芳烃的扩散及活性位的可接触性,从而促进初始转化率的提高。样品经酸处理脱铝后,单位酸密度降低,有效抑制了双分子反应的发生及焦炭前躯体的形成,提高了活性稳定性。由于介孔结构的引入和酸密度的优化,四氢萘在碱-酸连续处理的样品上初始转化率较处理前提升近20%,目的产物选择性提高9%,同时显著改善了催化稳定性。

A series of modified mordenite zeolite catalysts were prepared Framework Atoms Extraction by desilication and dealumination,and systematically characterized by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),Inductively coupled plasma atomic emission spectrometry(ICP),27Al nuclear magnetic resonance(27Al NMR),27Si nuclear magnetic resonance(27Si NMR),scanning electron microscope(SEM),transmission electron microscope(TEM)and nitrogen adsorption-desorption,etc.The results demonstrated that the controllable desilication and dealumination could efficiently extract the Si atoms and Al atoms from framework to introduce mesoporisity and adjust acidity,respectively.In tetralin catalytic cracking,the introduction of mesoporisity and acid density increase of alkali treated samples can effectively improve the diffusivity of polycyclic aromatic hydrocarbons and the accessibility of active sites,thus promoting the initial conversion.Attributed to the extraction of framework aluminum atoms,the acid density decrease of acid treated sample leaded to effective inhibition of bimolecular reactions and the formation of coke precursor,thus improving the catalysis stability.Combined the advantages of the mesoporisity introduced by Si atoms extraction and the optimization of acid density by the subsequent Al atoms extraction,the initial conversion of tetralin catalytic cracking over the desilicated-dealuminated samples increased by nearly 20%and the selectivity of target products especially mononuclear aromatics enhanced by 9%compared with the parent one,and a significantly improvement was obtained on catalytic stability.