Adsorption on alumina

Veljkovic, S. R., and S. M. Milenkovic, Concentration of Carrier-free Radioisotopes by Adsorption on Alumina, in Proc. of the 2nd UN Conference on Peaceful Uses of Atomic Energy. Vol. 20, pp. 45-49, United Nations (1958). 

Antia et al. [96] proposed a colorimetric method comprising a concentration step and a reaction with 2,7-dihydroxynaphthalene. This method has a detection limit of 0.1 mg/1. Methods comprising concentration by adsorption on alumina, followed by elution and colour development, yielded a detection limit of 5 ng/1 [97,98]. These methods have not been too successful in hands other than those of the original authors, possibly because of the amount of manipulation necessary in the analysis. 

Figure 6.6 Demonstration of the retardation of Pt adsorption on alumina by high ionic strength (a) 1 1 electrolytes ...

With the RPA model it has been possible to simulate many sets of CPA/alumina data mentioned in the literature [18], with the same set of unadjusted parameters (PZC, K and K2, OH density). Since pH shifts in the presence and the absence of CPA adsorption on alumina [23] and PTA adsorption on silica [19] are similar, it can be concluded that metal and proton transfer are independent in these systems. Thus the pH shift model can be used in concert with the RPA model not only to predict metal uptake, but also to compute final pH from the initial pH of the contacting solutions [18,28],... 

Adsorption of a surfactant on solids is dependent, among other things, on the structure of both the hydro-phobic and hydrophilic portions of it. There are a number of mechanisms proposed for surfactant adsorption and an understanding of the effects of the structure of the surfactant can help in elucidating the role of these mechanisms. In this study, the effect on adsorption on alumina of some structure variations of sulfonates (chain length and the branching and the presence of ethyoxyl, phenyl, disulfonate and dialkyl groups) is examined above and below CMC as a function of surfactant concentration, pH and salinity. Co-operative action between an ionic alkyl sulfonate and a nonionic ethoxylated alcohol is also studied. 

Figure 4. Effect of CioSO. concentration on CioSQ- adsorption on alumina in a mixture with CiaSO.,.

Fio. 33. CD adsorption on alumina-supported platinum (40) and palladium (42) characterized by ATR-IR spectroscopy during catalysis. Top spectra taken at different CD concentrations in hydrogen-saturated CH2CI2. The CD concentration increases from bottom to top (0-3 x 10 M for platinum and 0 4.3 X 10 M for palladium). Vibrational bands indicative of various adsorption modes of CD (bottom) are marked. Bands indicative of species 2 are absent from spectra observed for CD adsorption on palladium (40,42). 

C-Tracer studies of acetylene adsorption on alumina- and silica-sup-ported palladium [53,65], platinum [66] and rhodium [53] show the coexistence of at least two adsorbed states, one of which is retained on the surface, the other being reactive undergoing molecular exchange and reaction with hydrogen. Acetylene adsorption exhibits the same general characteristics as those observed with ethylene (see Sect. 3.2). However, there are important differences. The extent of adsorption and retention is substantially greater with acetylene than with ethylene. Furthermore, the amounts of acetylene retained by clean and ethylene-precovered sur-... 

The greater amount of retention observed with acetylene than with ethylene has been ascribed to the ability of the former to polymerise extensively. The existence of surface polymers following acetylene adsorption on alumina- and silica-supported platinum [60], evaporated palladium films [154] and silica-supported rhodium [67] has been demonstrated by thermal desorption studies. 

Many laboratory accidents have been ascribed to presence of peroxides in solvents, usually, but not exclusively ethers. Storage of the solvents for over-long periods, often under poor conditions, is a common feature of the incidents. When peroxides are removed from solvents by chromatographic adsorption on alumina columns, the concentrated band of strongly adsorbed peroxides at the top of the column may become hazardous if the solvent evaporates [1], The use of self-indicating molecular sieve under nitrogen is described as an effective method of de-peroxidising THF, diethyl and dipropyl ethers, suitable also for bulk-scale operations [2]. 

Azimonti, G., Bidoglio, G., Righetto, L., and Bellobono, I. R. (1994). Cobalt and mercury adsorption on alumina colloids in the presence of humic substances. In Humic Substances in the Global Environment and Implications to Human Health, Senesi, N., and Miano, T. M., eds., Elsevier, Amsterdam, 1079-1084. 

Thus, adsorption of NH3 on alumina resembles that of water in many respects. Both molecules are adsorbed molecularly at low temperatures but are chemisorbed dissociatively at higher temperatures. Ammonia is held strongly on A1203 surfaces and cannot be removed completely even on desorption at 500°C. Various species occur simultaneously, their relative importance being determined by the OH content of the surface. Furthermore, displacement adsorptions may take place. Thus, NH2" ions readily replaced chloride ions on surfaces of chlo-rided aluminas (166). One has, therefore, to conclude that ammonia retention on aluminas cannot be an acceptable measure of surface acidity and can hardly be related to catalytic activity. Ammonia adsorption on aluminas as studied by infrared spectroscopy, perhaps combined with TPD experiments (173), gives ample information on surface properties but ammonia cannot be used as a specific poison on alumina. 

Although a variety of amines, particularly trimethylamine and n-butylamine have widely been used as poisons in catalytic reactions and for surface acidity determinations (20), comparably few spectroscopic data of adsorbed amines are available. As with ammonia, coordinatively adsorbed amines held by co-ordinatively unsaturated cations have preferentially been found on pure oxides (176, 193-196), whereas the protonated species were additionally observed on the surfaces of silica-aluminas and zeolites (196-199). However, protonated species have also been detected on n-butylamine adsorption on alumina (196) and trimethylamine adsorption on anatase (176) due to the high basicity of these aliphatic amines. In addition, there is some evidence for dissociative adsorption of n-butylamine (196) and trimethylamine (221) on silica-alumina. Some amines undergo chemical transformations at higher temperatures (195, 200) and aromatic amines, such as diphenylamine, have been shown to produce cation radicals on silica-alumina (201, 201a). 

The formation of methane has been proved by Fink (245, 246) and Deo et at. (247) by mass spectrometry to occur on acetone adsorption on alumina. This surface reaction thus lends some support to the assumption of basic OH" ions on the surface of alumina and titanium dioxide (see Sections IV.D.l and 2). 

It thus follows from the foregoing discussion that C02 adsorption on alumina is a key compound for the study of the chemical nature of a variety of distinct surface sites. However, it is also apparent that unambiguous conclusions can hardly be drawn from C02-poisoning experiments due to manifold, simultaneously existing surface species. 

Separation of Methylated Methylglycosides by Adsorption on Alumina. A New Method for End-group Determinations in Methylated Polysaccharides, J. K. N. Jones, J. Chem. Soc., (1944) 333-334. 

Mohamed, R.S., Neves, G.B.M., Kieckbusch, T.G. 1998. Reduction in cholesterol and fractionation of butter oil using supercritical CO2 with adsorption on alumina. Int. J. Food Sci. Technol. 33, 445—454. 

J.A.R. van Veen et al, Chemistry of (phospho-)molybdate adsorption on alumina surfaces, J. Phys. Chem., 94 (1990) 5275-5285. 

In recent years the fast fluidized bed has also found applications in other processes, such as low-temperature adsorption of pollutants (e.g, HC1, HF, S02) from different process waste gas streams (Reh, 1986), noise reduction (Yang, 1992), etc. for example, in the aluminum smelter of VAW/Lurgi today, 3 x 106 m3/hr of fluorine-laden potline offgas are cleaned to less than 1 mg F/m3 by adsorption on alumina at a temperature of 70°C. 

In the following section, CO adsorption on alumina supported palladium nanoparticles of various sizes and surface structures is examined and compared with the corresponding results for CO on Pd(l 11) and rough Pd(l 11) (119,120,152,289). The preparation and characterization of the alumina support and of deposited palladium nanoparticles have been described in detail (63,68,73,83,101,290) and only a brief summary is given here. 

A similar investigation was carried out by Kfirkela and Kulonen (1959) who partially hydrolyzed elastin by acids, alkalies, and enzymes under varying conditions and fractionated the products by adsorption on alumina and elution with ammonia. They obtained fractions in which the yellow color was enriched and determined the infrared and ultraviolet absorption spectra. They concluded that the yellow pigment was tightly bound to the peptide chain and that it did not appear to be a bile pigment. 

S-Alkylcysteine C-S Lyase (EC 4.4.1.6). The endosperm of seeds of the shrub Albizzia lophanta contains djenkolic acid (HOOCCH(NH2)-CH2SCH2SCH2CH(NH2)C00H) and an enzyme which cleaves it to pyruvate, ammonia, and highly odoriferous substances (CH2(SH)2 ) (48, 49). The enzyme has been purified 200-fold by acid and heat treatment, (NH4)2S04 precipitation, and adsorption on alumina (50). It has a broad specificity and cleaves S-derivatives of L-cysteine, its sulfoxide, and sulfone. L-Cysteine itself is cleaved to pyruvate, HjS, and ammonia. 

Different mechanisms of H3PO4 adsorption on alumina are proposed in the literature ... 

The adsorption of molybdates in the presence of phosphorus oxo-species in solution (or those already deposited on an alumina support) or vice versa (i.e., adsorption of phosphate on a Al—Mo support) has also been explored. For example, Fig. 20 shows the isothermal adsorption on alumina supports of solutions containing different concentrations of ammonium heptamolybdate (AHM). From Fig. 20a, which corresponds to the sequential impregnation steps whereby phosphorus is adsorbed first (before molybdenum), it is clear that molybdenum is adsorbed in lower amounts on the Al—P support than on the phosphorus-free alumina. However, the amount of molybdenum adsorbed on the Al—P support also depends on the pH of the AHM solution (Fig. 20b). Molybdenum oxo-species tend to adsorb in greater amounts on the Al—P support under acidic condition. 

Water adsorption on alumina leads to molecular adsorbates [110]. There are some reports on the formation of isolated hydroxyl groups on regular sites [113, 114]. Whether they are the results of dissociative water adsorption is not completely clear, although there is a recent theoretical paper that predicts the dissociation of water on Al203(0001) by protonation of a surface oxygen, while the molecule previous to dissociation resides on a cation site [115]. There is no experimental verification of this result as yet. There are, however, explored routes to hydroxylate alumina surfaces either by exposure to atomic hydrogen or by a combination of aluminium deposition and subsequent hydrolyzation with water [116]. 

Fig. 13.10. Effect of pH on the extent of chloroplatinic acid adsorption on alumina. (Redrawn using data from Ref. 80.)...

The required conditions for adsorption on alumina are anionic precursors at a pH lower than eight or cationic precursors at a pH higher than eight. Adsorption of chloroplatinic acid fails into the first category and can take place even in an acidic medium. 3 Interaction of alumina with Pt(NH3)4(OH)2 and Pt(NH3)4Cl2 in ammonia fits in the second. A solution of sodium chloroplatinate is, however, not sufficiently acidic so the pH is higher than eight and anionic adsorption does not take place. ... 

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