Infrared alumina

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... 

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 time necessary for completion of the reaction may vary from 0.5 to 4 hours, depending on the actual activity of the alumina. The progress of conversion should be monitored by infrared analysis of a concentrated sample of the solution. Stirring should be continued for 15 minutes after the nitroso band at 1540 cm. has disappeared. A strong diazo band at about 2100 cm. will then be present. The carbonyl band at 1750 cm. initially due to nitrosocarbamate, will usually not disappear completely during the reaction, because some diethyl carbonate is formed in addition to carbon dioxide and ethanol. Diethyl carbonate is removed during the work-up procedure. 

A mixture consisting of 0.69 g (10.5 mmoles) of zinc-copper couple, 12 ml of dry ether, and a small crystal of iodine, is stirred with a magnetic stirrer and 2.34 g (0.7 ml, 8.75 mmoles) of methylene iodide is added. The mixture is warmed with an infrared lamp to initiate the reaction which is allowed to proceed for 30 min in a water bath at 35°. A solution of 0.97 g (2.5 mmoles) of cholest-4-en-3/ -ol in 7 ml of dry ether is added over a period of 20 min, and the mixture is stirred for an additional hr at 40°. The reaction mixture is cooled with an ice bath and diluted with a saturated solution of magnesium chloride. The supernatant is decanted from the precipitate, and the precipitate is washed twice with ether. The combined ether extracts are washed with saturated sodium chloride solution and dried over anhydrous sodium sulfate. The solvent is removed under reduced pressure and the residue is chromatographed immediately on 50 g of alumina (activity III). Elution with benzene gives 0.62 g (62%) of crystalline 4/5,5/5-methylene-5 -cholestan-3/5-ol. Recrystallization from acetone gives material of mp 94-95° Hd -10°. 

Many methods have been used to determine the deuterium eontent of hydrogen gas or water. For H2/D2 mixtures mass speetroseopy and thermal eonduetivity ean be used together with gas ehromatography (alumina aetivated with manganese ehloride at 77 K). For heavy water the deuterium eontent ean be determined by density measurements, refraetive index ehange, or infrared speetroseopy. 

The application of infrared photoacoustic spectroscopy to characterize silica and alumina samples is reported. High quality infrared photoacoustic spectra illuminate structural changes between different forms of silica and alumina, as well as permit adsorbate structure to be probed. Adsorption studies on aerosil suggest adsorbed species shield the electric fields due to particle-particle interactions and induce changes in the vibrational spectra of the adsorbates as well as in the bulk phonon band. It is shown that different forms of aluminum oxides and hydroxides could be distinguished by the infrared spectra. 

The infrared spectra for various aluminum oxides and hydroxides are shown in Figure 3. Figure 3a is a-alumina (Harshaw A13980), ground to a fine powder with a surface area of 4 m /g. The absorption between 550 and 900 cm is due to two overlapping lattice modes, and the low frequency band at 400 cm is due to another set of lattice vibrations. These results are similar to those obtained by reflection measurements, except that the powder does not show as... 

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. 

The results obtained for the various aluminum oxides and hydroxides indicate that infrared photoacoustic spectroscopy may be useful in characterizing structural transformations in these species. Very clear differences between a-alumina and y-alumina were noted in the region of the lattice vibrations. The monohydrate, boehmite, showed a very distinct Al-OH stretching feature at 1070... 

The results presented here for silicas and aluminas illustrate that there is a wealth of structural information in the infrared spectra that has not previously been recognized. In particular, it was found that adsorbed water affects the lattice vibrations of silica, and that particle-particle Interactions affect the vibrations of surface species. In the case of alumina, it was found that aluminum oxides and hydroxides could be distinguished by their infrared spectra. The absence of spectral windows for photoacoustic spectroscopy allowed more complete band identification of adsorbed surface species, making distinctions between different structures easier. The ability to perform structural analyses by infrared spectroscopy clearly indicates the utility of photoacoustic spectroscopy. 

This latter point was stressed by some of us in a recent report studying NO storage and reduction on commercial LSR (lean storage-reduction) catalysts, in order to catch valuable information about the behaviour of typical NO storage materials in real application conditions. Nature, thermal stability and relative amounts of the surface species formed on a commercial catalyst upon NO and 02 adsorption in the presence and in the absence of water were analysed using a novel system consisting of a quartz infrared reactor. Operando IR plus MS measurements showed that carbonates present in the fresh catalyst are removed by replacement with barium nitrate species after the first nitration of the material. Nitrate species coordinated to different barium sites are the predominant surface species under dry and wet conditions. The difference in the species stabilities suggested that barium sites possess different basicity and, therefore, that they are able to stabilize nitrates at different temperatures. At temperatures below 523 K, nitrite species were observed. The presence of water at mild temperatures in the reactant flow makes unavailable for NO adsorption the alumina sites [181]. 

Catalyst Pd-45 was made by boiling a suspension of alumina P 110 (Degussa) with a solution of Na PdCfi. After 1 hr the pH of the slurry was brought to a value of 6-7 by addition of NaHCOs. Boiling was continued for half an hour, after which the specimen was filtered off, washed and dried at 120°C. It was reduced in the infrared apparatus for 2 hr at 450°C. 

In order to correlate this model reaction with physicochemical techniques, 2,6-dimethylpyridine and carbon dioxide adsorption followed by Infrared spectroscopy [2-4] which are generally used to respectively characterize the acidity and the basicity of aluminas were also undertaken. 

Adsorptions of probe molecules followed by Infrared were also carried out in order to estimating the acidity and the basicity of aluminas. Carbon dioxide and 2,6-dimethylpyridine were respectively used for the basicity and the acidity. Figure 3 reports the results obtained. 

In this paper we will first describe a fast-response infrared reactor system which is capable of operating at high temperatures and pressures. We will discuss the reactor cell, the feed system which allows concentration step changes or cycling, and the modifications necessary for converting a commercial infrared spectrophotometer to a high-speed instrument. This modified infrared spectroscopic reactor system was then used to study the dynamics of CO adsorption and desorption over a Pt-alumina catalyst at 723 K (450°C). The measured step responses were analyzed using a transient model which accounts for the kinetics of CO adsorption and desorption, extra- and intrapellet diffusion resistances, surface accumulation of CO, and the dynamics of the infrared cell. Finally, we will briefly discuss some of the transient response (i.e., step and cycled) characteristics of the catalyst under reaction conditions (i.e.,... 

The catalyst was prepared by impregnating y-alumina (Alon) to incipient wetness using an aqueous solution of (PtClg). After impregnation, the powder was dried, and calcined in air at 773 K (500°C) for 2 h. The infrared disc was prepared by compressing 0.08 g of the catalyst powder at 58 840 N. The properties of the catalyst disc are listed in Table I. 

The high sensitivity of tunneling spectroscopy and absence of strong selection rules allows infrared and Raman active modes to be observed for a monolayer or less of adsorbed molecules on metal supported alumina. Because tunneling spectroscopy includes problems with the top metal electrode, cryogenic temperatures and low intensity of some vibrations, model catalysts of evaporated metals have been studied with CO and acetylene as the reactive small molecules. Reactions of these molecules on rhodium and palladium have been studied and illustrate the potential of tunneling spectroscopy for modeling reactions on catalyst surfaces,... 

D. X. Liu, J. X. Gao, C. J. Murphy, and C. T. Williams, In situ attenuated total reflection infrared spectroscopy of dendrimer-stabilized platinum nanoparticles adsorbed on alumina, J. Phys. Chem. B 108, 12911-12916(2004). 

In a detailed infrared spectroscopic study. Peri and Hannan (333) confirmed the existence of at least three types of isolated hydroxyl groups on y-alumina. 

Most of the work with alumina was done, however, attempting to elucidate the nature of the catalytically active sites in dehydrated alumina. The catalytic activity of alumina is enhanced by treatment with hydrofluoric acid. Oblad et al. (319) measured a higher activity in the isomerization of 1- and 2-pentene. Webb (339) studied the effect of HF treatment on ammonia adsorption by alumina. There was no difference in the capacity. However, the ammonia was more easily desorbed at a given temperature from the untreated sample. Apparently, the adsorption sites grew more strongly acidic by the treatment. No NH4+ ions, only NHj molecules were detected by their infrared spectra, indicating that the ammonia was bound by Lewis acids rather than Bronsted acids. 

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. 

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