MORDENITE ACIDITY - DEPENDENCE ON THE SI/AL RATIO AND THE FRAMEWORK ALUMINUM TOPOLOGY .2. ACIDITY INVESTIGATIONS

被引:55
作者
STACH, H
JANCHEN, J
JERSCHKEWITZ, HG
LOHSE, U
PARLITZ, B
HUNGER, M
机构
[1] CENT INST PHYS CHEM,O-1199 BERLIN,GERMANY
[2] UNIV LEIPZIG,DEPT PHYS,LEIPZIG,GERMANY
关键词
D O I
10.1021/j100200a051
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The acidity of a series of mordenites dealuminated by acid refluxing was studied by calorimetric measurements of the NH3 chemisorption, protein magic angle spinning nuclear magnetic resonance spectroscopy, and temperature-programmed desorption of NH3 and NH4+ ion exchange. The number of bridged OH groups determined by H-1 MAS NMR corresponds to the number of tetrahedrally coordinated Al atoms. Starting with a low Al content (a high Si/Al ratio), the number of the strong acidic sites increases with increasing Al number of the framework up to 4.6 Al atoms/u.c. (Si/Al ratio of 9.5) and then decreases. The decrease of the strong acidity above 4.6 Al atoms/u.c. may be explained by the appearance of an aluminum atom in the second coordination sphere of the Si-OH-Al group. The experimentally found value of the maximum (at m = 0.096) in the curve of the strong acidity versus the aluminum molar fraction coincides with a value calculated by Barthomeuf from the topological Al density of mordenite, thus confirming her theoretical concept of zeolite acidity.
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页码:8480 / 8485
页数:6
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