Hydroxylation, IR spectra

Information about the number and types of hydroxyl groups present in a particular zeolite can be obtained from its IR spectrum. Si-OH-Al groups in different locations in a zeoHte structure can have different stretching frequencies. Figure 4.23 shows the hydroxyl IR spectra for several different zeolites. Both the FAU and... 

Calcined and steamed FAU samples also have complex hydroxyl IR spectra. Figure 4.25 shows the difference between an ammonium ion-exchanged FAU before and after steaming and calcination. The very simple, easily interpretable hydroxyl spectrum of the ammonium exchanged FAU sample is transformed into a complex series of overlapping hydroxyl bands due to contributions from framework and non-framework aluminum atoms in the zeolite resulting from the hydrothermal treatment conditions [101]. 

Figure 16.1 Hydroxyl IR spectra of stabilized Ys S-1, steamed at 750°C S-2, steamed and acid-washed.

The hydroxyl IR spectra of sihca activated at high temperatures are relatively simple. All authors detect a sharp band at 3750-3740 cm that is normally extended to lower frequencies. The density of the silanols on samples... 

Infrared The IR spectra of phenols combine features of those of alcohols and aro matic compounds Hydroxyl absorbances resulting from O—H stretching are found m the 3600 cm region and the peak due to C—O stretching appears around 1200-1250 cm These features can be seen m the IR spectrum of p cresol shown m Figure 24 3... 

Beyer synthesis, 2, 474 electrolytic oxidation, 2, 325 7r-electron density calculations, 2, 316 1-electron reduction, 2, 282, 283 electrophilic halogenation, 2, 49 electrophilic substitution, 2, 49 Emmert reaction, 2, 276 food preservative, 1,411 free radical acylation, 2, 298 free radical alkylation, 2, 45, 295 free radical amidation, 2, 299 free radical arylation, 2, 295 Friedel-Crafts reactions, 2, 208 Friedlander synthesis, 2, 70, 443 fluorination, 2, 199 halogenation, 2, 40 hydrogenation, 2, 45, 284-285, 327 hydrogen-deuterium exchange, 2, 196, 286 hydroxylation, 2, 325 iodination, 2, 202, 320 ionization constants, 2, 172 IR spectra, 2, 18 lithiation, 2, 267... 

Morterra and Low109,110 proposed that thermal crosslinking may occur between 300°C and 500°C where phenolic hydroxyl groups react with methylene linkages to eliminate water (Fig. 7.43). Evidence for this mechanism is provided by IR spectra which show decreased OH stretches and bending absorptions as well as increased complexity of the aliphatic CH stretch patterns in this temperature range. 

Scheme 2 is still oversimplified, because it does not take into consideration that the two silicon atoms directly involved in the hydroxyl condensation are also linked to other rings in a three-dimensional mode and that part of the surface strain could be localized on these rings. The appearance in the IR spectra of new vibrations in the 880-940 cm region, attributed to the modes of strained siloxane bridges in two membered rings [26,28-32], well evidences this fact. 

Fig. 3 represents the IR spectra in the hydroxyl region and in the OH bending region for the activated 4A and 5A zeolite samples. The outgassed 5A 86 sample IR spectrum exhibits a weak absorption at 3744 cm 1 which corresponds to non acidic external silanol groups and a large contribution between 3700 cm 1 and 3500 cm 1 (Fig. 3a). This... 

Figure 3 IR spectra in the hydroxyl region and in the OH bending region for the 4A and 5 A zeolite samples after activation at 450°C.

Prior to solving the structure for SSZ-31, the catalytic conversion of hydrocarbons provided information about the pore structure such as the constraint index that was determined to be between 0.9 and 1.0 (45, 46). Additionally, the conversion of m-xylene over SSZ-31 resulted in a para/ortho selectivity of <1 consistent with a ID channel-type zeolite (47). The acidic NCL-1 has also been found to catalyze the Fries rearrangement of phenyl acetate (48). The nature of the acid sites has recently been evaluated using pyridine and ammonia adsorption (49). Both Br0nsted and Lewis acid sites are observed where Fourier transform-infrared (FT IR) spectra show the hydroxyl groups associated with the Brpnsted acid sites are at 3628 and 3598 cm-1. The SSZ-31 structure has also been modified with platinum metal and found to be a good reforming catalyst. 

Characterization of the donor bound polymers follows from their spectroscopic (ir and uv-vis KBr) properties in comparison with the starting donor monomers, and from elemental analyses. That the donors are covalently bound to the polymer and not present as unreacted monomers can be seen by the absence of the characteristic monomer functional group absorption (i.e. -OH, COzH) in the donor bound polymer. For example in Figure 1, the comparative ir spectra of p-hydroxyphenyl-TTF monomer and this donor covalently bound to linear and to cross-linked polysytrene are given. Except for the presence of the hydroxyl absorption in the monomer, all three spectra are essentially identical, indicating a rather clean polymer attachment reaction. 

Figure 4.23 IR spectra showing hydroxyl region ofvarious H-form zeolites. Samples...

Figure 4.25 IR spectra showing hydroxyl region of H-FAU samples showing the effect of steaming and calcination.

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