摘要
本文应用^(29)Si,^(27)Al MAS NMR和XRD技术,测量了四种不同脱铝深度的稀土超稳Y沸石的骨架硅铝比,得到了一致的结果,并研究了稀土超稳Y沸石的脱铝过程和稀土离子稳定Y沸石骨架铝的机理.发现稀土离子存在时,Y沸石骨架中Si、Al的分布与相同硅铝比的HY不同,在浅、中度脱铝时,主要脱除的是Si(2Al)和Si(3Al)中的铝,深度脱铝时,主要是脱除Si(1Al)和少量Si(2Al)中的铝,而Si(3Al)几乎不变,提出稀土离子最可能是位于方钠石笼的Si(3Al)附近,平衡三个AlO_4^-四面体上的负电荷,起到稳定Si(3Al)结构单元的作用.其次,稀土超稳Y沸石中总的非骨架铝(N_(Al))_EF,随脱铝深度的增加而增加,仅只在REUSY-38的^(27)Al MAS NMR谱中观察到Al^(a+)非骨架铝的存在.
For four REUSY zeolites, the framework (Si/Al)_F ratio were measured by ^(?)Si MAS, NMR, XRD, techniques, and obtained the agreeable results. The change of distribution of Si and Al of framework during dealumination and the mechanism of stabilizing the framework aluminum by rare-earth ions were also investigated by ^(29)Si MAS-NMR. It was found that when the range of (Si/A1)_F is from 2.6 to 4.0, the aluminums in Si (2Al) and Si (3Al) are mainly removed, if the (Si/Al)_F is from 4.0 to 6.0, the aluminums removed are mainly that of Si (1A1) and a little of Si (2A1). Comparing the relative populations of Si(0Si)_(4-n)-(0A1)_n in framework struoture of REUSY zeolites with that of in framework of HY zeolite, it was found that the distribution of framework Si and Al for both Y zeolites are very different, particularly for Si (3A1)in REUSY zeolites, its relative population are changed slightly at the whole range of dealumination. It means that the possible positions of rare-earth ions are near the Si (3A1) and equalize the negative charges of three tetrahedral AlO_4^-, thus the Si (3A1) unites can be stabilized by rare-earth ions. For the four REUSY zeolites, the total extra-framework aluminums (N_(Al))_(EF) increase with the increase of depth of dealumination, the (N_(AI))_(EF) appeared as Al^(3+) are only observed in ^(27)Al MAS-NMR of REUSY-38 spectrum.
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
1992年第7期637-642,共6页
Acta Chimica Sinica
基金
国家自然科学基金
抚顺石油化工研究院资助课题
