改性Y分子筛的酸碱性能及吸附性能的研究

Studies on Acidity and Basicity and Adsorption of Modified Y Zeolites

吡啶、吡咯、苯、甲苯、乙苯作为探针分子,在Li+,Na+,K+,Cs+改性的Y型分子筛上进行吸附,用TPD及IR方法系统地研究了不同碱金属离子改性的Y型分子筛的酸碱性能和吸附性能的变化.结果表明,按Li、Na、K、Cs的顺序,随着碱金属离子半径的增大,其L酸酸强度依次减弱,L碱的强度逐渐增强.由于改性Y型分子筛所含碱金属离子的不同,其对芳烃的吸附的强弱及吸附量的大小亦不同.随着骨架外的阳离子的半径逐渐增大,碱的强度逐渐增强,与芳烃的作用愈强烈,导致TPD脱附峰温增高及芳烃和侧链上的C-H伸缩振动谱带向低波数位移愈多.由于位阻的原因,对含同一种碱金属离子的分子筛来说,随着芳烃侧链C数的增加,芳烃的吸附量逐渐减小.

The acidity and basicity of alkali cation exchanged Y zeolites were investigated systematically using pyridine and pyrrole as the TPD and IR spectroscopic probe respectively. It was found that the overall Lewis basicity in the modified Y zeolites increased and the Lewis acidity in the modified Y zeolites decreased as the cation was exchanged from LiY to CsY in the alkali cation series. The adsorption of benzene, toluene and ethylbenzene on Y zeolites modified by alkali cations were also studied comparatively by IR spectroscopy and TPD. The following results were obtained: (1) The adsorption of pyridine on modified Y zeolites could also be used to characterize the acidity and basicity of alkali cation exchanged Y zeolites; (2) The C - H stretching frequencies of aromatic ring, of CH3 on the side-chain of toluene, and of - CH2 - on the side-chain of ethylbenzene shifted towards lower wavenumber as the cation was exchanged from LiY to CsY; (3) The adsorption strength and the amount of sorbed aromatics on modified Y zeolites were related to the basicity of alkali cation exchanged Y zeolites.