Alumina infrared spectra

XI-1C) as well as alongside it. The infrared spectrum of CO2 adsorbed on 7-alumina suggests the presence of both physically and chemically adsorbed molecules [3]. 

Still another type of adsorption system is that in which either a proton transfer occurs between the adsorbent site and the adsorbate or a Lewis acid-base type of reaction occurs. An important group of solids having acid sites is that of the various silica-aluminas, widely used as cracking catalysts. The sites center on surface aluminum ions but could be either proton donor (Brpnsted acid) or Lewis acid in type. The type of site can be distinguished by infrared spectroscopy, since an adsorbed base, such as ammonia or pyridine, should be either in the ammonium or pyridinium ion form or in coordinated form. The type of data obtainable is illustrated in Fig. XVIII-20, which shows a portion of the infrared spectrum of pyridine adsorbed on a Mo(IV)-Al203 catalyst. In the presence of some surface water both Lewis and Brpnsted types of adsorbed pyridine are seen, as marked in the figure. Thus the features at 1450 and 1620 cm are attributed to pyridine bound to Lewis acid sites, while those at 1540... 

Dehydration of gibbsite under pressure in moist air produces boehmite (aluminum oxide mono-hydrate). An infrared spectrum of boehmite (Kaiser substrate grade alumina) is shown in Figure 3c. 

Further dehydration of boehmite at 600 0 produces y-alumina, whose spectrum is shown in Figure 3b. There is a loss in surface area in going from boehmite to y-alumina. The sample shown here has a surface area of 234 m /g (this sample was obtained from Harshaw A23945 the calcined Kaiser substrate gave an identical infrared spectrum). The y-alumina sample shows two major differences from o-alumina. First, there is a more intense broad absorption band at 3400 cm" due to adsorbed water on the y-alumina. Second, the y-alumina does not show splitting of the phonon bands between 400 and 500 cm" as was observed for o-alumina. The y-alumina is a more amorphous structure and has much smaller crystallites so the phonon band is broader. The y-alumina also shows three features at 1648, 1516 and 1392 cm" due to adsorbed water and carbonate. 

Parry (344) determined the infrared spectrum of pyridine adsorbed on rj-alumina dehydrated at 450°. Characteristic differences in the 1400-1700 cm region exist in the spectra of pyridine adsorbed via hydrogen bonds, pyridinium ions, and pyridine coordinately bonded to electrophilic sites. Pyridinium ions are characterized by a strong band at 1540 cm and a very strong band at 1485-1500 cm" coordinately bonded pj ridine has a strong absorption at 1447-1460 cm". No evidence was found for the existence of Bronsted sites on the alumina surface. 

The orange solid product was washed with water, dried in vacuum over P205, and chromatographed on an alkaline alumina column. The first fraction, 420 mg., yellow to pale orange crystals eluted with pentane-benzene, proved to be the principal constituent of the mixture. It was recrystallized from pentane-benzene to give a nearly colorless compound, m.p., 162.5°-163° C. Its infrared spectrum was identical with that of triphenylcarbinol, lit. m.p., 162.5° C. (11). 

Figure 12.12B Infrared spectrum of synthetic Li/A) hydrotalcite deposited by impregnation on alumina (I mg 3(X) mg of KBr).

Infrared spectrum of pyridine adsorbed on undoped alumina-supported vanadium oxide catalyst, after evacuation at 150 °C, shows an absorption band at 1450 cm 1, characteristic for pyridine retained on Lewis acid sites, which has been related to V-free alumina [4,10, 11]. The intensities of the bands at 1450 cm l (related to Lewis acid sites) and 1545 cm I (related to Bronsted acid sites) have been used to determine the numer of Lewis and Bronsted acid sites on the surface of catalysts. The results are outlined in Table 1. 

A sample of hydrated alumina was exposed to glacial acetic acid overnight and then sucked dry. Before acid treatment, its infrared spectrum between 3800-1200 cm l consisted solely of broad hydrate water peaks (3450 and 1630 cm l). After treatment new peaks at 2920, 2850, 1575, 1465, 1415, and 1335 cm appeared, all assignable to acetate ion. No signs of unionized acid carbonyl (1760 and 1710 cm for monomer and dimer respectively) was seen. Mass gain and BET surface area measurements indicated a monolayer to be present (See... 

The strong inhibiting effect of water during the reduction of well-dispersed iron oxide phases on alumina surfaces is also apparent from the infrared spectrum of carbon monoxide adsorbed onto the reduced catalyst prepared from complex iron cyanides according to the above procedure of Boellaard and co-workers Despite the support, the size of the iron particles, and the loading of iron on the support all being essentially the same, the infrared spectrum of the adsorbed carbon monoxide is completely different. The absorption band at 2155 cm is not seen, which indicates that Fe(II) is not present at the alumina surface when reduced in the presence of low partial pressures of water vapor. Rather than bands with frequencies above about 2000 cm bands at 1806, 1884, and 1984 cm are observed (Fig. 5.9). Even at room temperature, disproportionation of carbon monoxide to carbon dioxide and carbon occurs, which is demonstrated by the presence of carbon dioxide adsorbed onto the alumina support. The infrared bands peaking at 1348 and 1598 cm arise from carbon dioxide adsorbed on alumina. 

Acetaldehyde is converted into high polymer at 203 K in the presence of alumina as catalyst.C0O3 and M0O3 also give high polymers in much smaller yields. Polyacetaldehyde is a white, non-sticky and hi y elastic material, whose structure is shown to be methylpolyoxymethylene by the infrared spectrum. The cationic mechanism has been suggested for the polymerization. ... 

Neodymium and YAG Lasers. The principle of neodymium and YAG lasers is very similar to that of the ruby laser. Neodymium ions (Nd +) are used in place of Cr + and are often distributed in glass rather than in alumina. The light from the neodymium laser has a wavelength of 1060 nm (1.06 xm) it emits in the infrared region of the electromagnetic spectrum. Yttrium (Y) ions in alumina (A) compose a form of the naturally occurring garnet (G), hence the name, YAG laser. Like the ruby laser, the Nd and YAG lasers operate from three- and four-level excited-state processes. 

The vibrational spectrum of 4-pyridine-carboxylic acid on alumina in Fig. 4d is equivalent to an infrared or Raman spectrum and can provide a great deal of information about the structure and bonding characteristics of the molecular layer on the oxide surface. For example, the absence of the characteristic > q mode at 1680 cm 1 and the presence of the symmetric and anti-symmetric O-C-O stretching frequencies at 1380 and 1550 cm indicate that 4-pyridine-carboxylic acid loses a proton and bonds to the aluminum oxide as a carboxylate ion. 

On the basis of the mechanism used to explain the band shifts and the ratio of bridged to linear carbon monoxide it is evident that the infrared spectra of chemisorbed carbon monoxide would be useful in studies of the carrier effect. When alumina is used instead of silica as a carrier for platinum the resulting spectrum of chemisorbed carbon monoxide shows that the band due to linear carbon monoxide has shifted to lower frequency and the amount of bridged carbon monoxide is increased (4). This is interpreted as showing that the n-type conductivity of the alumina is sufficient to modify the electronic properties of the platinum. 

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