无溶剂合成多级孔ZSM-5分子筛及丙烷芳构化反应性能研究

Solvent-free Synthesis of Hierarchical ZSM-5 Zeolite for Propane Aromatization

以无溶剂合成方法,利用生物质多糖海藻酸钠制备了具有多级孔道结构的ZSM-5分子筛。采用XRD、SEM、TEM、FT-IR和N2吸附-脱附等多种表征技术对合成分子筛进行了表征,探究了海藻酸钠的添加量对分子筛形貌、孔结构、比表面积等物化性质的影响。结果表明,通过添加海藻酸钠制备的ZSM-5分子筛是具有丰富的多级孔结构,其添加量显著影响分子筛的形貌和孔结构,进而影响其在丙烷芳构化反应中的稳定性和芳构化选择性。该分子筛经Zn改性后用于丙烷芳构化反应,显示出良好的催化性能,其中样品Zn/ZSM-5-SA-16.7的丙烷转化率最初达87.2%,反应进行24 h后,丙烷转化率仍能达到50%以上,并且保持了较高的芳烃选择性(接近60%)。引入介孔结构有利于提高微孔分子筛内有机大分子的扩散速率和催化剂活性位的可接近性,降低副反应的发生,进而提高催化剂的选择性和反应稳定性。

Hierarchical ZSM-5 zeolites have been synthesized by adopting biomass polysaccharide sodium alginate as macroporous and mesoporous template through the solvent-free synthesis method.All the samples were characterized by XRD,SEM,TEM,FTIR and Nadsorption-desorption,and the effects of sodium alginate/SiOweight ratio was studied,and the obtained materials exhibit different morphology,pore structure and surface area by varying the amount of SA in the initial synthesis mixture. The results show that ZSM-5 zeolites prepared by adding SA possess abundant multi-stage pore structure,which affects the stability and selectivity of ZSM-5 catalysis in propane aromatization reaction. The obtained ZSM-5 zeolites modified by Zn showed excellent catalytic performance in propane aromatization reaction.The propane conversion of Zn/ZSM-5-SA-16.7 sample was87.2% initially,and the propane conversion was still more than 50% after 24 h of reaction, and the aromatic hydrocarbon selectivity was close to 60%. The hierarchical zeolite show excellent catalytic performance in the catalytic reactions involving macromolecules due to improving the diffusion rate of macromolecules and the accessibility of the active sites of the catalyst,thus reducing the occurrence of side reactions.