氧化镁改性对纳米HZSM-5分子筛催化甲醇制丙烯的影响

采用浸渍法制备了一系列不同Mg含量(0-8%,w)的改性纳米HZSM-5分子筛.利用X射线衍射(XRD)、铝固体魔角旋转核磁共振(27AlMASNMR)、N2吸附/脱附、氨-程序升温脱附(NH3-TPD)和吡啶吸附傅里叶变换红外(FT-IR)光谱等技术对改性前后样品的结构和酸性进行了详细表征;并在常压、500℃和甲醇空速(WHSV)为1.0h-1的反应条件下,在连续流动固定床反应器上考察了其对甲醇制丙烯反应的催化性能.结果表明,随着Mg含量的增加,丙烯和丁烯的选择性逐渐增大,而甲烷、乙烯和芳烃的选择性逐渐降低.催化剂的稳定性先随Mg含量的增加而增加,当Mg含量为2%时达到最大,之后又随Mg含量的增加而降低.MgO改性对纳米HZSM-5分子筛催化性能的影响主要是由其酸性和织构性能的改变而引起的.

Effect of Magnesium Oxide Modification on the Catalytic Performance of Nanoscale HZSM-5 Zeolite for the Conversion of Methanol to Propylene

A series of nanoscale HZSM-5 zeolites modified with different amounts (0-8%, w) of magnesium were prepared by an impregnation method and characterized by X-ray diffraction (XRD), Al solid state magic angle spinning nuclear magnetic resonance (²⁷Al MAS NMR), N₂-adsorption/desorption, temperature-programmed desorption of NH₃ (NH₃-TPD), and pyridine adsorption Fourier transform infrared (FT-IR) methods. The conversion of methanol to propylene was tested in a continuous flow fixed-bed microreactor at atmospheric pressure, 500 ℃, and a methanol space velocity (WHSV) of 1.0 h^-1. The results indicated that with an increase in the amount of Mg, the selectivity of propylene and butene increased but those of methane, ethylene and aromatics decreased consistently. With an increase in the amount of Mg the stability of the catalyst was found to increase initially, pass through a maximum at 2% and then decrease with higher amounts of Mg. The effect of modification with magnesium oxide on the catalytic performance of the nanoscale HZSM-5 zeolite for the conversion of methanol to propylene can be attributed to the resultant changes in acidity and texture of the modified nanoscale HZSM-5 zeolites.