Fluorinated zeolites catalytic activity

The importance of recognizing and dealing with zeolite synthesis as a kinetic process that involves the isolation of metastable phases is pointed out in this book in a variety of ways. An examination of the extensive scientific and patent literature on zeolite synthesis rapidly convinces one that a lack of understanding of this point has been a major bottleneck in the characterization of zeolite chemical and physical properties. The zeolite properties are defined not only by synthesis parameters, but also by treatment following synthesis for example, most synthesis treatment of zeolites with fluorine can be used to modify hydrophobicity drastically and increase catalytic activity for n-butane cracking. 

Dilute fluorine gas (0-20%) can be used to treat zeolites at near-ambient temperature and pressure. Most of the resulting materials retain very high crystallinity even after 600°C postcalcination for two hours. Both framework infrared spectra and X-ray powder diffraction patterns clearly show structural dealumination and stabilization. The hydrophobic nature of the fluorine-treated and 600sC-calcined material is shown by a low water adsorption capacity and selective adsorption of n-butanol from a 1 vol.% n-butanol-water solution. Fluorination also changes the catalytic activity of the zeolite as measured by an n-butane cracking method. 

We believe the use of a direct gaseous phase fluorination process for modifying the surface and structure of zeolites to be a new process (18). The literature does contain references to the use of hydrogen fluoride (20, 22, 23), boron trifluoride (21, 24), aluminum monofluoride (sic) (19) and silica difluoride (sic) (19) to treat the surface of a zeolite to obtain higher catalytic activity. However, the use of fluorine gas to modify both surface and structure has not been reported before. The purpose of this paper is to report results of fluorination of zeolites and to describe the process involved in such a treatment. Detailed results on fluorine-treated zeolites and their unusual properties, both adsorptive and catalytic, will be discussed in forthcoming papers. 

As the data in Table VI show, the catalytic activity of the fluorinated zeolites can be either drastically increased or decreased depending on the treatment conditions and post-fluorination treatment. Varying the treatment conditions should allow the catalytic activity of a zeolite to be modified as desired. 

Phthalocyanine complexes within zeolites have also been prepared by the ship-in-a-bottle method (see Section 6.6), and have subsequently been investigated as selective oxidation catalysts, where their planar metal-N4 centres mimic the active sites of enzymes such as cytochrome P450, which is able to oxidize alkanes with molecular oxygen. Cobalt, iron and ruthenium phthalocyanines encapsulated within faujasitic zeolites are active for the oxidation of alkanes with oxygen sources such as iodosobenzene and hydroperoxides. Following a similar route, Balkus prepared Ru(II)-perchloro- and perfluorophthalocyanines inside zeolite X and used these composites for the selective catalytic oxidation of alkanes (tert-butylhydroperoxide). The introduction of fluorinated in place of non-fluorinated ligands increases the resistance of the complex to deactivation. 

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