不同脱铝深度稀土超稳Y沸石的酸性质

用FT-IR和NH_2-TPD研究了稀土含量相同时脱铝程度不同的四种REUSY沸石的酸性质. 并对复杂羟基谱的归属进行了讨论. 同时将酸性质与骨架的Si、Al分布, 非骨架组份以及二次孔相关联, 提出浅、中度脱铝时主要脱除与超笼中HFOH相关联的Si(3Al)和Si(2Al)单元中的Al, 深度脱铝时则脱除与六方柱笼和方钠石笼中LFOH 羟基相关联的Si(1AI)中的铝和少量Si(2Al)中的铝. 另外发现, 非骨架组份使一部分HFOH羟基不能被吡啶分子接近. 而二次孔的形成使一部份LFOH 能被吡啶分子接近. 随着脱铝深度的加深, 总酸、B酸、L 酸量都减少. 但强酸和B酸的强度均相应增加.

STUDIES ON ACIDIC PROPERTIES OF VARIOUS REUSY

The acidic properties of four REUSY zeolites were studied by NH_3-TPD and IR spectra. The results show that the spectra of hydroxyl groups of REUSY are very complicated. It can be distinguished as three kinds of hydroxyl groups i.e. silicon hydroxyl groups, high frequency hydroxyl groups and low frequency hydroxyl groups. The acidic or nonacidic hydroxyl groups can also be seperated by the IR differential spectra. When the acidic properties were related to the distribution of framework silicon and aluminum and extraframework aluminun measured by ~(29)Si and ~(27)Al MAS NMR, and also to the secondary mesopores formed in the process of dealumination, it was found that when (Si/Al)_F is about 3 to 4, the acid sites corresponding to the Si(3Al) or Si(2Al) are mainly removed from the α-cages. As the (Si/Al) decreases with the Si(2Al) are removed from the β-cages and hexagonal cages. The results also show that a portion of framework acidic high frequency hydroxyl groups can not be accessed by pyridine molecules, but the low frequency hydroxyl groups can be accessed by Py molecules due to the formation of secondary mesopores. On dealumination, the Bronsted, Lewis and the total acid sites all decrease, and the strength of strong acid sites and Bronsted acid sites increase.