DEALUMINATED ZEOLITES, SPECTROSCOPIC STUDIES

Marqnes, J.P., Gener, I., Ayrault, P, Bordado, J.C., Lopes, J.M., Ramoa Ribeiro, R, and Guisnet, M. Infrared spectroscopic study of the acid properties of dealuminated BEA zeolite. Micropor. Mesopor. Mater. 2003, 60, 251-262. 

Phosgene proved to be an appropriate reactant to remove aluminium from the zeolite framework [1,2]. Detailed measurements have been carried out to investigate the adsorption of phosgene [3], the mechanism of dealumination by infrared spectroscopic and thermogravimetric methods [4], structural consequences [5], adsorption and catalytic properties of modified mordenites [6]. In addition an NMR study has been carried out, to measure the thermal stability of so-called hydroxy nests in H-mordenite dealuminated with phosgene [7]. 

The acidity of many zeolites has been studied after various treatments (heating, cation exchange, various dealuminations, incorporation in the framework of other atoms...). This is described elsewhere in the book. Only a few examples are given here showing how spectroscopic investigations can be conducted to provide new information. 

Fejes et al. [50-54] extensively studied the extractive dealumination of zeolites (mordenite) with acid halides (phosgene, nitrosyl chloride) at 400-600 C. The reaction of H-mordenite with phosgene, monitored by IR spectroscopic determination of the volatile reaction products HCl and C02> was foimd to proceed in three main steps at temperatures above 100 C (Eq. 2a) and 300°C (Eqs.2b and 2 c) ... 

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