Isopropanol, adsorption

Zaki, M Hu.s.sein, G El Ammawy, II Mansour, S Polz, J Kndzinger, H, Effect of foreign ion additives on ceria surface reactivity towards isopropanol adsorption and dccompt)sition an infrared investigation. Journal of Molecular Catalysis., 1990 57, 367-378. 

Isopropanol adsorption was performed at several temperatures in order to determine the more suitable conditions for the alcohol chemisorption on the active sites avoiding further reaction. The observation that no molecular isopropanol is detected in the TPSR spectra indicates that no physisorption (or weak chemisorption) of the alcohol is produced even at 313 K over heteropolyacids (spectra not shown). The maximum amount of surface isopropoxy species over tungsten oxide WO3 and monolayer supported tungsten oxide species was obtained through isopropanol adsorption at 383 and 343 K, respectively. 

The number of available surface sites for isopropanol adsorption of bulk tungsten trioxide and monolayer supported tungsten oxide catalysts, even mesoporous nanoparticles, is orders of magnitude (0.9-6 pmol/m ) lower than the heteropolyacids (8-55 pmol/m ). This observation cannot be attributed to the surface structure because all these materials possess polymerized WOg species with octahedral coordination (see Table 5.1). Moreover, no correlation is observed with the specific surface area and the pore diameter because high surface area, mesoporous monolayer supported catalysts possess lower Ns than HPAs. In fact. Table 5.1 shows that those materials do not possess microporosity the specific surface area is only external surface area. This observation shows that the adsorption of alcohol occurs exclusively at the outermost surface layer of WO3 and monolayer supported tungsten oxide catalysts. 

This information suggests that isopropanol adsorption on y-alumina Involves more than one adsorption band, i.e. both hydroxyl and emthyl groups are bonded and likely to different sites on the surface of alumina. 

Isopropanol Adsorption over One-Component Bulk Metal... 

Maximum Number of Active Sites for Isopropanol Adsorption of WO3, Monolayer Supported Tungsten Oxide on T1O2, Phospho-Tungstic Keggin and Wells-Dawson Acids... 

Isopropanol adsorption (at 40 C) and TPSR analysis was performed on the fully hydrated acid and after in situ calcination at 70, 115, and 320°C in order to obtain more insights on the role of the degree of hydration on the catalytic activity of the phospho-tungstic Wells-Dawson type acid. 

Examples of mono-layer adsorption isotherms obtained for chloroform and butyl chloride are shown in Figure 5. The adsorption isotherms of the more polar solvents, ethyl acetate, isopropanol and tetrahydro-furan from -heptane solutions on silica gel were examined by Scott and Kucera [4]. Somewhat surprisingly, it was found that the experimental results for the more polar solvents did not fit the simple mono-layer... 

The chromatographic resolution of bi-naphthol enantiomers was considered for simulation purposes [18]. The chiral stationary phase is 3,5-dinitrobenzoyl phenyl-glycine bonded to silica gel and a mixture of 72 28 (v/v) heptane/isopropanol was used as eluent. The adsorption equilibrium isotherms, measured at 25 °C, are of bi-Langmuir type and were proposed by the Separex group ... 

The separation of bi-naphthol enantiomers can be performed using a Pirkle-type stationary phase, the 3,5-dinitrobenzoyl phenylglycine covalently bonded to silica gel. Eight columns (105 mm length) were packed with particle diameter of 25 0 fiva. The solvent is a 72 28 (v/v) heptane isopropanol mixture. The feed concentration is 2.9 g for each enantiomer. The adsorption equilibrium isotherms were determined by the Separex group and already reported in Equation (28) [33]. 

The analytical methods for a-sulfo fatty acid esters reported in the literature deal with the determination of the surfactants in different matrices like detergents or product mixtures from the fabrication. The methyl esters of a-sulfo fatty acids can be separated from a mixture of different surfactants together with sulfonated surfactants by adsorption on an anionic exchanger resin such as Dowex 1X2 or 1X8. Desorption from the exchanger resin is successful with sodium hydroxide (2%) in a 1 1 mixture of isopropanol and water [105]. 

Nanoparticles of the semicondnctor titanium dioxide have also been spread as mono-layers [164]. Nanoparticles of TiOi were formed by the arrested hydrolysis of titanium iso-propoxide. A very small amount of water was mixed with a chloroform/isopropanol solution of titanium isopropoxide with the surfactant hexadecyltrimethylammonium bromide (CTAB) and a catalyst. The particles produced were 1.8-2.2 nm in diameter. The stabilized particles were spread as monolayers. Successive cycles of II-A isotherms exhibited smaller areas for the initial pressnre rise, attributed to dissolution of excess surfactant into the subphase. And BAM observation showed the solid state of the films at 50 mN m was featureless and bright collapse then appeared as a series of stripes across the image. The area per particle determined from the isotherms decreased when sols were subjected to a heat treatment prior to spreading. This effect was believed to arise from a modification to the particle surface that made surfactant adsorption less favorable. 

Alcohols are hydroxylated alkyl-compounds (R-OH) which are neutral in reaction due to their unionizable (OH) group (e.g., methanol, ethanol, isopropanol, and w-butanol). The hydroxyl of alcohols can displace water molecules in the primary hydration shell of cations adsorbed onto soil-solid and sediment-solid clay particles. The water molecule displacement depends mainly on the polarizing power of the cation. The other adsorption mechanisms of alcohol hydroxyl groups are through hydrogen bonding and cation-dipole interactions [19,65],... 

Because of the problems encountered with the water system, the use of aliphatic alcohols, ie.g., methanol, ethanol, and isopropanol, as modifiers of the adsorption strength has been recommended (44. 45. 50. 51). Usually, between 0.01 and 0.5% (v/v) alcohol is added to the eluent. As an example, the k values for the benzyl alcohols on a silica column are in the same range when eluted with dichloromethane containing either 0.1% water (50% water-saturated) or 0.15% methanol or 0.3% isopropanol (45). The preparation and preservation of these alcohol-eluent mixtures is accompanied by problems similar to those discussed with water-modified eluents. Also, column equilibration is slow (44). The efficiency of columns operated with alcohol-modified eluents is generally lower than that of water-modulated eluent system. At some alcohol concentrations, distorted peaks with tailing or frontal asymmetry have been observed 44), but olhei workers using another silica could not verify this observa tion (61). 

Tween 85 is used extensively for RME [84]. Russell and coworkers [234] used Tween 85/isopropanol microemulsions in hexane to solubilize proteins and not only showed >80% solubilization of cytochrome C at optimum conditions, but also proved that Tween 85 does not have a detrimental effect on the structure, function, and stability of subtilisin and cytochrome C. There are other reports available on the extraction and purification of proteins using Tween 85-RMs and also on the stability of protein activity in these systems [234]. It has also been shown that Tween 85-RMs can solubilize larger amounts of protein and water than AOT. Tween 85 has an HLB of 11, which indicates that it is soluble in organic solvents. In addition, it is biodegradable and can be successfully used as an additive in fertihzers [235,236]. Pfammatter et al. [35] have demonstrated that RMs made of Tween 85 and Span 80 can be successfully used for the solubilization and growth of whole cells. Recently, Hossain et al. [84] showed an enhanced enzymatic activity of Chromobacterium viscosum Hpase in AOT/Tween 85 mixed reverse micellar systems when compared to that in classical AOT-RMs. This is due to the modification of the interface in AOT-RMs caused by the co-adsorption of Tween 85, and increased availability of the oHve oil molecules (substrate) to the enzyme. 

Ai and Suzuki [5,9] investigated the combination V2Os—P2Os. The acidity was measured indirectly by the activity for dehydration of isopropanol and was shown to decrease with increasing P2Os content. The activity for the oxidation of butene-1 and butadiene to maleic acid anhydride decreased accordingly. It was shown that the adsorption equilibrium constant of the olefin on the catalyst also decreased in the same way. 

The effects of post-synthesis alumination on purely siliceous MCM-41 material with A1(NC>3)3 on acidity have been studied by FTIR, NH3-TPD, and IPA decomposition reaction. The FTIR results of pyridine absorption show that both Lewis and Bronsted acid sites are increased by the post-modification. The amount of NH3 adsorbed on the alumina-modified MCM-41 samples increases with the loading of Al onto the surface of MCM-41. Due to the improved acidity, the alumina-modified MCM-41 materials show considerably higher catalytic activity for dehydration of isopropanol than purely siliceous MCM-41. In addition, XRD and N2 adsorption results show that all MCM-41 samples maintained their uniform hexagonal mesoporous structure well after they have been subjected to post-synthesis alumination with the loading of Al species on Si-MCM-41 varied from 0.1 wt. % up to 10 wt. % (calculated based on AI2O3). 

Post-synthesis alumination using A1(N03)3 as the precursor improves the acidity of siliceous MCM-41 materials significantly. FTIR results show that both Bronsted and Lewis acid sites are increased upon alumination. The number of acid sites increases with the Al content on MCM-41. NH3-TPD reveals the mild strength of these created acid sites. Due to the improved acidity, the catalytic activity for dehydration of isopropanol to propylene over these alumina-modified MCM-41 materials is considerably promoted by post-synthesis alumination. The results of XRD and N2 adsorption show that the enhancement of acidity for siliceous MCM-41 by postsynthesis alumination does not cause any serious structural deformation of the resulting material. 

In addition to quinone reduction and hydroquinone oxidation, electrode reactions of many organic compounds are also inner-sphere. In these charge transfer is accompanied by profound transformation of the organic molecules. Some reactions are complicated by reactant and/or product adsorption. Anodic oxidation of chlorpro-mazine [54], ascorbic acid [127], anthraquinone-2,6-disulfonate [128], amines [129], phenol, and isopropanol [130] have been investigated. The latter reaction can be used for purification of wastewater. The cyclic voltammogram for cathodic reduction of fullerene Cm in acetonitrile solution exhibits 5 current peaks corresponding to different redox steps [131]. 

Munuera and Stone (142) successfully applied the model of a (110) plane to their adsorption studies of water, isopropanol, and acetone. The dry (110) face exposes 5.1 five-coordinate Ti4+ ions. Half of these were able to chemisorb water dissociatively, leading to the formation of two types of surface OH groups. The activation energy for desorption of this water was 107 kJ mole-1. At this state of hydroxylation the rutile surface consists of isolated five-coordinated Ti4+ ions, which on further addition of water coordinate water molecu-larly, of isolated O2- ions, and of pairs of OH groups, one being monodentate and the other bidentate with respect to the cations. 

VOv supported on ai2o3 VO, supported on silica, ceria, alumina, zirconia, niobia, titania-silica, zirconia-silica VOr supported on alumina, silica Dehydration Dehydration at 773 K in 02/He, methanol adsorption 02/He at 773 K, adsorption of isopropanol... 

Vinyl acetate-ethyl acetate Propane-propylene Ethanol-isopropanol Hydrochloric acid-water Nitric acid-water Close-boiling Close-boihng Close-boihng Maximum-boiling azeotrope Maximum-boiling azeotrope Phenol, aromatics Acrylonitrile Methyl benzoate Sulfuric acid, calcium chloride for salt process Sulfuric acid, magnesium nitrate for salt process Alternative to simple distillation Alternative to simple distillation, adsorption Alternative to simple distillation Sulfuric acid process rehes heavily on boundary curvature Sulfuric acid process rehes heavily on boundary curvature... 

A similar technique has been used to determine the acidic character of niobium oxide and niobyl phosphate catalysts in different solvents (decane, cyclohexane, toluene, methanol and isopropanol) using aniline and 2-phenyl-ethylamine as probe molecules [27, 28]. The heat evolved from the adsorption reaction derives from two different contributions the exothermic enthalpy of adsorption and the endothermic enthalpy of displacement of the solvent, while the enthalpy effects describing dilution and mixing phenomena can be neglected owing to the differential design and pre-heating of the probe solution. 

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