摘要
采用27Al MAS NMR、N2吸附-脱附、IR等表征技术及XRD Rietveld结构精修的方法,通过清除和交换引入非骨架铝,探讨了USY沸石中非骨架铝的形态。结果表明,27Al MAS NMR化学位移为0的非骨架铝以游离在超笼中的非骨架铝为主,化学位移为30-50的非骨架铝与沸石骨架存在键合作用;晶体学可识别的离子态非骨架铝存在于方钠石笼的SⅠ′和SⅡ′位置,其中,SⅠ′位置的非骨架铝与沸石骨架3个O3原子及与其配位的三重轴的O形成不稳定的四配位结构,SⅡ′位置的Al不与沸石骨架O形成配位。超笼中未发现可识别的离子态非骨架铝。聚合态非骨架铝的存在将堵塞沸石孔道,影响微孔吸附性能,并掩盖B酸中心。清除非骨架铝后,可以使沸石孔道畅通,使B酸中心得到恢复。
The type and the chemical state of non-framework aluminum and the related influence on zeolite acidity were investigated by means of ^27Al MAS NMR, N2 adsorption-desorption, XRD Rietveld refinement. The results showed that non-framework aluminum corresponding to the chemical shift of 0 in .^27Al MAS NMR existed in an isolate state in the supercage of USY zeolite and the non-framework aluminum corresponding to the chemical shift of 30-50 may be bound to Y zeolite framework. The crystallographically identifiable non-framework AP＋ located at SⅠ＇ and SⅡ＇ sites of the sodalite cage, and the non-framework Al^3＋ at S Ⅰ＇ site coordinates with three framework 03 atoms and one O atom at 111 ternary axis to form unstable four fold coordination structure, and the non-framework AP＋ at S Ⅱ＇ site could not coordinate with framework O atom. There was not any crystallographically identifiable non-framework Al^3＋ in the supercage. Polymeric non- framework aluminum blocked up pore channels of Y zeolite, influencing microporous adsorption ability and covering Bronsted acid sites. By removing polymeric non-framework aluminum, pore channels of Y zeolite became free from blockage and Bronsted acid sites were recovered.
出处
《石油学报（石油加工）》
EI
CAS
CSCD
北大核心
2007年第2期1-7,共7页
Acta Petrolei Sinica(Petroleum Processing Section)
基金
国家科技部重点基础研究发展规划项目(G2000048001)资助
关键词
Y沸石
非骨架铝
结构精修
B酸
L酸
Y zeolite
non-framework aluminum
Rietveld refinement
Bronsted acid
Lewis acid
