小晶粒ZSM-5沸石的绿色、经济性合成（英文）

Green and Cost-Effective Preparation of Small-Sized ZSM-5

通过添加少量silicalite-1做为活性晶种在较宽的SiO_2/Al_2O_3比范围内制备得到了小晶粒ZSM-5沸石,对所得样品进行X射线衍射(XRD),扫描电子显微镜(SEM),透射电子显微镜(TEM),N_2吸附-脱附,氨程序升温脱附(NH3-TPD)以及吡啶吸附红外(Py-IR)表征。研究结果表明活性晶种能有效导向生成ZSM-5沸石,避免杂晶形成并可减小所得沸石的晶粒尺寸;所得ZSM-5在低硅铝比(SiO_2/Al_2O_3 ratio=30)时呈纳米颗粒聚集体形貌,具有多级孔道结构性质;在较高硅铝比时(SiO_2/Al_2O_3 ratio=60–120)呈小晶粒形貌,颗粒尺寸大约200 nm。值得注意的是由胶态晶种引入的少量TPAOH不完全堵塞沸石的微孔孔道,因此所得所有沸石均无需提前焙烧除去模板剂即可进行离子交换得到具有酸性的H型ZSM-5沸石,所得酸性H型ZSM-5沸石具有和常规方法得到的相同SiO_2/Al_2O_3比的ZSM-5相似的酸类型、强度和酸量,在催化甲醇转化制备烯烃时呈现出相似的甲醇转化率和烯烃选择性。与常规ZSM-5制备方法比较,该方法能够大大减少模板剂的使用量,避免了样品离子交换前的焙烧,方法绿色清洁、成本低廉,具有很好的潜在的工业应用前景。

Small-sized zeolite ZSM-5 for a wide SiO2/Al2O3 ratio range was prepared using a small amount of colloidal silicalite-1 as the active seeds. The thus-prepared small-sized ZSM-5 samples have been characterized using X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, N2 adsorption-desorption analysis, temperature-programmed ammonium desorption （NH3-TPD） analysis, and adsorbed pyridine infrared spectroscopy （Py-IR）. The use of the active silicalite-1 seeds was effective in directing the reaction towards the formation of the MFI phase, avoiding the impure phases and reducing the crystal sizes. The prepared sample exhibited aggregated morphologies when a lower ratio of starting batch SIO2/Al2O3 （SIO2/Al2O3 ratio = 30） was used. The aggregates, with the size of -500 nm, were formed with nano-sized primary crystals 50 nm in size, possessing large external surface area （84.9 m2.g^-1）and secondary pore volume （0.22 cm3.g^-1） and relatively regular mesopores. Different morphologies could be observed when the SIO2/Al2O3 ratio was increased （SiO2/Al2O3 ratio = 60 120）. ZSM-5 with the size of 200 nm could be prepared, with the external surface area and the secondary pore volume being -60 m2.g^-1 and 0.10 cm3.g^-1, respectively. It should be highlighted that all the prepared samples could be directly ion-exchanged to obtain the acidic H-form samples without complete blocking of the micropores due to the low dose of the organic structure-directing agent. The obtained acidic H-form samples exhibited acidic properties similar to the samples ion-exchanged after calcination and the conventional ZSM-5 possessing similar SiO2/Al2O3 ratio, showing catalytic performance comparative to the catalytic conversion of methanol to olefins. Compared with conventional methods, this method largely reduced the use of organic templates and avoided the subsequent combustion before ion-exchange. The method is green and cost-effective, possessing wide potentials in the industrial processes.