Alumina measuring surface area

Surface areas were determined by nitrogen sorption at -196 C using a S-point (p/pg = 0.06-0.21) BET calculation method Because KDT s can contain large ainounts of nonfromework alumina, as-measured surface areas tend to underestimate the concentration of the zeolitic constituent For this reason, surface areas are reported on both an as-nteasured m /g product) and a "m /g framework basis For the latter, framework mass computations assumed that sll silica was in the zeolite framework, and that only framework aluminum contributed to sodium ion exchange capacity The "m /g framework" data should thus be considered reasonable estimates rather than accurate values ... 

The porous alumina catalyst was supplied by B. I. Parsons, Department of Energy, Mines and Resources, Ottawa, Canada. It had a measured surface area of 220 m2/g (one-point isotherm), and a slurry of the material in distilled water had a pH of 10.0. The pore size varied between 1000 and 400A, and the pore volume was 1.9 ml/g (5). The active alumina was manufactured by the Aluminum Co. of America, Portland, Ore. 

The surface areas of cylindrical or pseudocylindrical pores are bound to decrease when increasing amoimts of strongly adsorbed matter are applied fissure-shaped capillaries should not show such an effect. Recently Fortuin has obtained some promising results with the lauric acid method of measuring surface areas on well-sintered samples of alumina, before and after the introduction of strongly bound OH-groups and water molecules (62). 

Using the weight changes from gibbsite to dehydrated sulphate and from sulphate to alumina, it was possible to obtain a measure of the conversion of gibbsite to sulphate and the effect of this on the properties of tlie alumina. A linear correlation was observed between conversion to sulphate and tlie surface area of the product alumina (Figure 2). At 100% conversion, aluminas of surface area of >120 m g could be produced by calcination. The alumina derived from Ajax aluminium sulphate had a surface area between 120 and 130 m. X-ray diffraction showed that y-alumina was the major product. 

In explosively shocked alumina Bergmann and Barrington ( ) found at least a 350% increase in line broadening, but only a modest 29% increase in the measured surface area which was reported as a consequence of shocking. In material sintered at 1600°C the shocked alumina was about 32% more dense than unshocked control specimens. (At lower sintering temperatures the effect of shocking presumably would have been even greater.) It was reported that... 

In this article, we will discuss the use of physical adsorption to determine the total surface areas of finely divided powders or solids, e.g., clay, carbon black, silica, inorganic pigments, polymers, alumina, and so forth. The use of chemisorption is confined to the measurements of metal surface areas of finely divided metals, such as powders, evaporated metal films, and those found in supported metal catalysts. 

As surface area and pore structure are properties of key importance for any catalyst or support material, we will first describe how these properties can be measured. First, it is useful to draw a clear borderline between roughness and porosity. If most features on a surface are deeper than they are wide, then we call the surface porous (Fig. 5.16). Although it is convenient to think about pores in terms of hollow cylinders, one should realize that pores may have all kinds of shapes. The pore system of zeolites consists of microporous channels and cages, whereas the pores of a silica gel support are formed by the interstices between spheres. Alumina and carbon black, on the other hand, have platelet structures, resulting in slit-shaped pores. All support materials may contain micro, meso and macropores (see text box for definitions). 

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... 

While our discussion will mainly focus on sifica, other oxide materials can also be used, and they need to be characterized with the same rigorous approach. For example, in the case of meso- and microporous materials such as zeolites, SBA-15, or MCM materials, the pore size, pore distribution, surface composition, and the inner and outer surface areas need to be measured since they can affect the grafting step (and the chemistry thereafter) [5-7]. Some oxides such as alumina or silica-alumina contain Lewis acid centres/sites, which can also participate in the reactivity of the support and the grafted species. These sites need to be characterized and quantified this is typically carried out by using molecular probes (Lewis bases) such as pyridine [8,9],... 

Fig. 6 (a) 2-D 7) maps, (b) their 1-D central cross sections, and (c) the 1-D profiles of hexachloroplatinate dianion distributions obtained by electron probe analyzer measurements. S-2 and S-3 identify different porous alumina pellets, both prepared with an egg-shell distribution of hexachloroplatinate dianion the dianion is located towards the external surface of the pellet). S-2 and S-3 differ in terms of their nominal diameter and their pore-size and surface-area characteristics. Reprinted with permission from ref. 24. Copyright (2000) American Chemical Society. 

The lipophilicity and specific hydrophobic surface area of 42 synthetic dyes were also measured on alumina-based RP-TLC layers as described above. The common and IUPAC names of the non-homologue series of synthetic dyes are compiled in Table 3.7. 

The polycrystalline platinum electrode was mounted in Kel>F resin and polished with a scries of alumina powders down to 0.05, resulting mirror finish. The apparent surface area was 1.85 cm. The electrode was washed with fuming sulfuric add and rinsed with ultra pure water prior to each measurement. 

The internal surface area of a porous inorganic membrane is often significantly affected by the heat treatment temperature. Leenaars, Keizer and Burggraaf (1984) have shown that, even if the crystallite size of the membrane precursor particles remains essentially the same (from the X-ray line-broadening measurements), the surfaee area of a transition-phase alumina membrane decreases with increasing calcination temperature. Con-... 

Ruthenium catalysts, supported on a commercial alumina (surface area 155 m have been prepared using two different precursors RUCI3 and Ru(acac)3 [172,173]. Ultrasound is used during the reduction step performed with hydrazine or formaldehyde at 70 °C. The ultrasonic power (30 W cm ) was chosen to minimise the destructive effects on the support (loss of morphological structure, change of phase). Palladium catalysts have been supported both on alumina and on active carbon [174,175]. Tab. 3.6 lists the dispersion data provided by hydrogen chemisorption measurements of a series of Pd catalysts supported on alumina. is the ratio between the surface atoms accessible to the chemisorbed probe gas (Hj) and the total number of catalytic atoms on the support. An increase in the dispersion value is observed in all the sonicated samples but the effect is more pronounced for low metal loading. 

Nienow (1983a) observed a delay in the start of particle growth when binder was added to a bed of porous particles and stable fluidization under conditions which produced quenching with non-porous particles. Nitrogen adsorption measurements showed that the pore surface area of alumina decreased as spraying proceeded, indicafing that an effective reduction in pore volume was taking place. 

There is no clear evidence to identify the active material for SO2 removal in a MgAl20 stoichiometric system. Figure 13 shows results for a 50-50 mole% magnesia-alumina material prepared from magnesium hydroxide and alumina sol and calcined at various temperatures. An attempt was made to correlate SO2 removal with compound formation, as measured by X-ray diffraction, and surface area. As indicated in the figure, SO2 removal ability decreased with Increasing calcination temperature as did surface area. X-ray diffraction analysis showed spinel formation increases as... 

The stability of MCM-41 is of great interest because, from the practical point of view, it is important to evaluate its potential application as a catalyst or adsorbent. It is known that purely-siliceous MCM-41 (designated here as PSM) has a high thermal stability in air and in oxygen containing low concentration (2.3 kPa) of water vapor at 700 °C for 2 h [1], However, the uniform mesoporous structure of PSM was found to be collapsed in hot water and aqueous solution due to silicate hydrolysis [2], limiting its applications associated with aqueous solutions. After MCM-41 samples were steamed in 100% water vapor at 750°C for 5 h. their surface areas were found to be lower than amorphous silica-alumina and no mesoporous structure could be identified by XRD measurement [3]. In addition, PSM showed poor stability in basic solution [4]. 

Alumina will also bind Cr03 and stabilize it to 900°C, and it can polymerize ethylene when reduced to Cr(II). High surface area y alumina can be made having the porosity necesssary for good activity. Besides the electronic differences between Si—O—Cr and A1—O—Cr bonds, such alumina catalysts typically have 50-100% more hydroxyl groups than silica at normal calcining temperatures. This is clear in Fig. 21, which shows the hydroxyl populations of three different supports. The hydroxyl concentration was measured by reaction with methylmagnesium iodide. 

The final coating thickness was adjusted by the amount of alumina in the aqueous suspension. The wash coats were calcined at 600 °C (step 6), which resulted in a porous coating with an internal surface area of approximately 70 m2 g 1 measured by BET surface analysis. 

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