Hydroxyl region

Infrared studies show that when water is adsorbed on the surface, the background intensity in the hydroxyl region increases new bands may appear but hydrogen-bonding effects make such conclusions uncertain. If such a catalyst is then exposed to hydrogen (or deuterium), no bands due to adsorbed hydrogen (or deuterium) are observed. Thus, adsorption of water apparently occurs on the active sites and blocks out type I chemisorption. 

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.

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.

Fig. 1 shows the increase of nitrite band near 780 cm- for various alcohol contents in ethylene-vinyl alcohol copolymers. The analysis of the hydroxyl region of the IR spectra (not shown) indicated that the reaction was not quantitative (residual OH band). The precise analysis of this band ( 34(X) 70 I / mol. cm) as w ell as the nitrite band (e780 639 I / mol. cm) allows to evaluate the reaction yield considering the total film thickness (Transmission 1R). The values decrease when the OH content increases (0.75 0.62 0.59 ans 0.59 for vinyl alcohol contents 2.6,4.9, 7.7 and 10.1% respectively). Complementary analysis by reflexion IR (HATR) showed that the first 5-8 pm (Germanium crystal) were fully transformed while the analysis of the first 20-25 pm (Zinc Selenide crystal) revealed a decrease of the yield from 1 to 0.5 when the alcohol content was increasing. Then, this treatment can be helpfull for surface modification of membranes. 

After the parent zeolites [3 with a Si/Al ratio of 15.20 (chemical analysis value) was treated with a NaB02 solution, the boronated sample was characterized by means of XRD, IR spectra in framework and hydroxyl regions and "Band 27AI MAS NMR techniques. It was found that BEA structure was essentially retained and no other phases were observed after the... 

The nature of the acidity of mordenite and its relation to catalytic activity have been investigated by Benesi (757), Lefrancois and Malbois (227) and Eberly et al. (225). Eberly et al. observed two absorption bands in the hydroxyl region of the infrared spectrum of H-mordenite. A band at 3740 cm-1 was attributed to silica-type hydroxyl groups, and a lower frequency band, 3590 cm-1, was thought to arise from hydroxyl groups associated with aluminum atoms in the structure. Acid extraction of the aluminum atoms from the framework, although leaving the structure intact resulted in a loss of the lower frequency hydroxyl band. 

Figure 4. Infrared spectra of the hydroxyl region for a SiClA-treated zeolite (series A, with Alf - 15.3) with various amounts of Na+ added as a poison (a) 0.02 wt% Na+, (b) 0.23 wt% Na+, (c) 0.49 wt% Na+. The ordinate is absorbance in arbitrary units. Reproduced with permission from Ref. 10. Copyright 1989 Academic Press.

Formation of a broad absorption band in the hydroxyl region of the infrared spectrum due to formation of defect sites or "hydroxyl nests" in dealuminated sites was introduced previously (1). 

The products discussed in this report are 22-68% aluminum depleted, relative to the respective starting materials, yet the hydroxyl region of the infrared spectrum shows that few hydrogen bonded OH groups were created as a result of the treatments (see the "z" values in the Tables). The value "z" is calculated from the measured absorbance at 3710 cm"1 in the hydroxyl region of the Infrared spectrum, compared to that measured for a standard sample with a known number of defect sites (1). "z" numerically... 

Figure 2. Comparison of the Hydroxyl Region Infrared Spectra of Some Titanium or Iron Substituted Zeolites with Untreated Starting Zeolites a and 50% AI-Depleted NaY.

Hydroxyl region infrared spectra of fluorine-treated zeolites... 

The infrared (IR) spectra recorded throughout irradiation show an increase in absorbance due to the formation of oxidized products. Because PS presents initial absorption bands in the carbonyl vibration region (1900-1500 cm-1), a subtraction of spectra has to be carried out in order to observe the shape of the carbonyl envelope due to the formation of the photoproducts (Figure 30.1). Several maxima or shoulders are observed in the carbonyl region at 1515, 1690, 1698, 1732 and 1785 cm-1. Another band with amaximumaround 1605 cm-1 isalsoobserved,even if the initial absorption of PS at 1603 cm-1 interfered in the subtraction. In the hydroxyl region, bands and shoulders at 3250,3450 and 3540 cm-1 are observed. 

Fourier transform (FT) IR analysis of the photooxidized SAN samples shows that the oxidation products formed in the copolymer may result not only from the oxidation of the styrene units, even in the first few hours of irradiation [11]. Figure 30.4 shows that the absorbance of the carbonylated photoproducts in the photooxidized SAN samples is different compared with PS (Figure 30.1). Substantial evidence for the contribution of the acrylonitrile units in the photooxidation was obtained by chemical and physical treatments carried out on pre-photooxidized samples as described above. For example, the SF4 treatment of a SAN photooxidized sample led to a partial decrease in absorbance in the hydroxyl region, corresponding to the disappearance of alcohols, hydroperoxides and acids. The absorbance remaining after treatment may be assigned to... 

The hydroxyl region revealed a broad absorption band with a maximum around 3430 cm-1 assigned to the convolution of hydroperoxides, alcohols and acids. 

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