Alumina study

Several reports have appeared over the last few years on the adsorption of organofunctional alkoxysilanes on alumina studied by IETS [2-14], Two general observations have emerged, namely ... 

So far, all the characteristics mentioned for monometallic-supported catalysts can be generalized for bimetallic systems. For instance, Pt-Ir on alumina, studied by Engels et al. 28), exhibited an enhancement of H2 adsorption (more than three times the sum of the individual capacities) for 80 % Pt 20 % Ir (by weight). Sinfelt and Via (29) also observed a rather high ratio [H/(Pt + Ir) = 1.7] for H2 chemisorption at room temperature on a series of Pt-Ir/alumina catalysts with low metal loading. They considered spillover as a possible explanation for the H/(Pt + Ir) ratio that they found. 

In neither case was it possible to propose definitive mechanisms due to the complexity of the systems in the 7-alumina study, it is suggested that adsorption-desorption processes are slow relative to rapid dismutation between two adsorbed species [105], while from the chromia study mono-molecular halogen exchange reactions with metal halide surface sites are indicated [38], The latter mechanism is reminiscent of the halogen exchange model proposed [95] for C2 CFCs on fluorinated chromia. 

All the forms of silica and silica-alumina studied are similar in the rates at which catalytic activity was induced in them by radiation (82). For instance, the yields of increased activity per unit dose were within a factor of about 100 of each other for silica gel, quartz, vitreous silica, cristobalite, and Cab-o-sil, although before irradiation the quartz and vitreous silica were lO to 10 times as active as any of the gels. In a series of experiments using reactor radiation in which silica gel was compared with silica-aluminas, the yield differed by less than a factor of 100. In other experiments the differences have been even less (83). These results are consistent with a single kind of defect being introduced at... 

There was a simple relationship between the rate of caprolactam formation over the range of modified aluminas studied and the surface concentration of intermediate strength acid sites, namely those from which ammonia desorbed in the temperature range 200-350°C. This relationship is shown in figure 6 and establishes a link between acidic sites of intermediate strength and caprolactam formation. Based on these data turnover frequencies were all in the range 0.8-1.8 x 10 3 molecules of caprolactam formed per surface site of intermediate acidity per second. 

Karlsson, L. M., and Liljeborg, A. (1994). Second-order stereology for pores in translucent alumina studied by confocal scanning laser microscopy. J. Microsc. (Oxford) 175, 186-194. 

Anionic Surfactants onto Canadian River Alluvium (CRA) and Alumina. The second study on gemini surfactants to be discussed was conducted in order to determine strategies for designing gemini surfactants in order to minimize adsorption. The adsorption studies were conducted on Canadian River alluvium (CRA) [9] and on alumina at room temperature. CRA is primarily a sand and is expected to behave similarly to sandstone cores. The anionic gemini surfaetants were supplied by DOW and used as received. The alkyl groups used in the CRA and alumina studies were linear and ineluded all l ehain lengths of C6, CIO, CI2, and C16. The DAMS components and the CI2 and C16 DADS were not studied due to their low water solubilities. 

M.F.Lausberg, E.M.Moroz, R.A.Shkrabina, V.A.Ushakov. "The thermal behaviour of doped alumina studied by XRD. I. La203-Al203". Appl.Cat., 1994, (in press). 

Concerning the effect of particle size and specific surface of alumina on FR properties, Cinausero [38] has studied four types of alumina with different morphologies. Table 12.2 gathers the parameters obtained for PMMA filled with 5 wt% of each alumina type in comparison with the pure PMMA sample. Note that all different aluminas studied have a spherical shape, except the NF type, which has a fibrous shape. 

Li C, Yan W, Xin Q (1994) Interaction of methane with surface of alumina studied by FT-IR spectroscopy. Catal Lett 24 249-256... 

Heeribout, L., Vincent, R., Batamack, R, Doremieux-Moiin, C., andRraissard, J. Bronsted acidity of amorphous silica-alumina studied by NMR. Catal Lett. 1998,53,23-31. 

The aluminas studied were Alcoa A-14, which had been elutriated to a particle size range of 3-5 // diameter, a high-purity powder prepared by calcining hydrated aluminum chloride which had been obtained by dissolving high-purity aluminum metal in HCl, Linde C1.0( ), and Alcoa 2456G ( ). The latter three powders were clustered, with ultimate particles of about 0.3, 0.3, and 5 // diameter, respectively. 

The tendency to form organized monolayers improves with chain length. This is illustrated in a study of adsorption kinetics in alkanoic acid monolayers on alumina by Chen and Frank [36]. They find that the Langmuir kinetic equation, discussed in Section XVII-3, (see Problem XI-6)... 

Surface heterogeneity may be inferred from emission studies such as those studies by de Schrijver and co-workers on P and on R adsorbed on clay minerals [197,198]. In the case of adsorbed pyrene and its derivatives, there is considerable evidence for surface mobility (on clays, metal oxides, sulfides), as from the work of Thomas [199], de Mayo and co-workers [200], Singer [201] and Stahlberg et al. [202]. There has also been evidence for ground-state bimolecular association of adsorbed pyrene [66,203]. The sensitivity of pyrene to the polarity of its environment allows its use as a probe of surface polarity [204,205]. Pyrene or ofter emitters may be used as probes to study the structure of an adsorbate film, as in the case of Triton X-100 on silica [206], sodium dodecyl sulfate at the alumina surface [207] and hexadecyltrimethylammonium chloride adsorbed onto silver electrodes from water and dimethylformamide [208]. In all cases progressive structural changes were concluded to occur with increasing surfactant adsorption. 

Similar, very detailed studies were made by Ebert [112] on water adsorbed on alumina with similar conclusions. Water adsorbed on zeolites showed a dielectric constant of only 14-21, indicating greatly reduced mobility of the water dipoles [113]. Similar results were found for ammonia adsorbed in Vycor glass [114]. Klier and Zettlemoyer [114a] have reviewed a number of aspects of the molecular structure and dynamics of water at the surface of an inorganic material. 

In view of the widespread use of nitrogen and argon in surface area and porosity studies, data for the construction of the standard a,-curves for these adsorbates on hydroxylated silica, are given in Table 2.14 (p. 93) for nitrogen and in Table 2.15 for argon. From the arguments of Section 2.12, these should be adequate for other oxides such as alumina, if high accuracy is not called for. 

A typical example, from the extensive study by Kamakin on an alumina-silica gel, is shown in Fig. 3.32. When the mercury pressure was reduced to 1 atm at the end of the first cycle, 27 per cent of the intruded mercury was retained by the sample a second intrusion run followed a different path from the first, whereas the second extrusion curve agreed closely with the first. Change in f re structure of the kind described above could perhaps account for the difference between the two intrusion curves, but could not explain the reproducibility of the remainder of the loop. There is no doubt that hysteresis can exist in the absence of structural change. 

A detailed study of the physical and chemical adsorption of water on three xerogels, ferric oxide, alumina and titania, as well as on silica (cf. p. 272) has been carried out by Morimoto and his co-workers. Each sample was outgassed at 600°C for 4 hours, the water isotherm determined at or near 20°C, and a repeat isotherm measured after an outgassing at 30 C. The procedure was repeated on the same sample after it had been evacuated at a... 

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethyl amine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcohoHc solution of ammonia and the mixture is heated to 50—75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated siHca—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH2CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

SHica—alumina has been studied most extensively. Dehydrated sHica—alumina is inactive as isomerisation catalyst but addition of water increases activity until a maximum is reached additional water then decreases activity. The effect of water suggests that Brmnsted acidity is responsible for catalyst activity (207). SHica—alumina is quantitatively at least as acidic as 90% sulfuric acid (208). 

The abihty of organically modified ceramics based on alumina, zkconia, titania, or siUca (and mixtures of each) to function as abrasion-resistant coatings has also been studied (62). Eor example, polycarbonate, when coated with an epoxy—aluminosihcate system, experiences a significant reduction in the degree of hazing induced by an abrader, as compared to uncoated polycarbonate. 

Chemical Raw Material. In addition to use as a catalyst raw material, clays are used or have been extensively studied as chemical raw material. For example, kaolin has been investigated as a raw material for aluminum metal production. Kaolin has a 38 to 40% alumina content and is available in the United States in large quantities whereas the higher alumina bauxite reserves are very limited. The Bureau of Mines has actively carried out research in the aluminum from ka olin area for many years. Activity increases whenever imports of bauxite are threatened by war or other trade intermptions (1,22,23). 

The vapor-phase esterification of ethanol has also been studied extensively (363,364), but it is not used commercially. The reaction can be catalyzed by siUca gel (365,366), thoria on siUca or alumina (367), zirconium dioxide (368), and by xerogels and aerogels (369). Above 300°C the dehydration of ethanol becomes appreciable. Ethyl acetate can also be produced from acetaldehyde by the Tischenko reaction (370—372) using an aluminum alkoxide catalyst and, with some difficulty, by the boron trifluoride-catalyzed direct esterification of ethylene with organic acids (373). 

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