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Ethylamine adsorption

We have prepared LDHs samples containing Ni and Mg as divalent cations, and A1 as trivalent cation, with different Mg/Ni ratios to modify the basicity of the solids. These samples have been studied in the gas phase hydrogenation of acetonitrile, and the liquid-phase hydrogenation of valeronitrile. The catalytic properties were correlated with reducibility of Ni particles, and acido-basicity of the surface probed by NH3 and ethylamine adsorptions. [Pg.298]

The molecular modelling approach, taking into account the pyruvate—cinchona alkaloid interaction and the steric constraints imposed by the adsorption on the platinum surface, leads to a reasonable explanation for the enantio-differentiation of this system. Although the prediction of the complex formed between the methyl pyruvate and the cinchona modifiers have been made for an ideal case (solvent effects and a quantum description of the interaction with the platinum surface atoms were not considered), this approach proved to be very helpful in the search of new modifiers. The search strategy, which included a systematic reduction of the cinchona alkaloid structure to the essential functional parts and validation of the steric constraints imposed to the interaction complex between modifier and methyl pyruvate by means of molecular modelling, indicated that simple chiral aminoalcohols should be promising substitutes for cinchona alkaloid modifiers. Using the Sharpless symmetric dihydroxylation as a key step, a series of enantiomerically pure 2-hydroxy-2-aryl-ethylamines... [Pg.57]

Samples, even at moderate concentrations, injected into the HPLC column may precipitate in the mobile phase or at the column frit. In addition, the presence of other compounds (e.g., lipids) in the injection sample may drive the carotenoids out of solution or precipitate themselves in the mobile phase, trapping carotenoids. It is best to dissolve the sample in the mobile phase or a slightly weaker solvent to avoid these problems. Centrifugation or filtration of the samples prior to injection will prevent the introduction of particles that may block the frit, fouling the column and resulting in elevated column pressure. In addition to precipitation, other sources of on-column losses of carotenoids include nonspecific adsorption and oxidation. These can be minimized by incorporating modifiers into the mobile phase (Epler et al., 1993). Triethylamine or diisopropyl ethylamine at 0.1% (v/v) and ammonium acetate at 5 to 50 mM has been successful for this purpose. Since ammonium acetate is poorly soluble in acetonitrile, it should be dissolved in the alcoholic component of the mobile phase prior to mixing with other components. The ammonium acetate concentration in mobile phases composed primarily of acetonitrile must be mixed at lower concentration to avoid precipitation. In some cases, stainless steel frits have been reported to cause oxidative losses of carotenoids (Epler et al., 1992). When available, columns should be obtained with biocompatible frits such as titanium, Hastolloy C, or PEEK. [Pg.872]

A graph similar to Figure 7 resulted with adsorption of tri-ethylamine onto the same iron oxide, with AHa< s=-13.1 Kcal/mole and Tm corresponding to 167 A2. Using Drago s values of Cg and Eg for triethylamine.il.09 and 0.99 respectively jin units of (Kcal/mole)V2>we can write equation (5) as ... [Pg.85]

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. [Pg.400]

One of the key advances in column technologies is the development of high-purity silica.1,9 In recent years, it has become a de facto industry standard for almost all new column offerings. This development stems from the realization that batch-to-batch reproducibility and peak tailing of basic solutes are mostly caused by acidic residual silanols. Figure 3.9 shows different types of silanols and their relative acidity. The worst culprits turned out to be the very acidic silanols adjacent to and activated by metallic oxides. Many older silica materials have high metallic contents (e.g., Spherisorb) and are extremely acidic. They often require the use of amine additives in the mobile phase (e.g., tri-ethylamine) to prevent adsorptive interaction with basic analytes. The inherent variations of these active (acidic) silanols are also responsible for the lack of batch-to-batch consistency of these acidic silica materials. [Pg.58]

The hydrogenation steps are the rate limiting steps over the fresh catalyst. After an experiment lasting two hours, we observed a dramatic decrease of the activity, specially of the MEA conversion and the disappearance of the intermediates. Furthermore, the main products, DEMA and DEA, were formed. These results show that the adsorption properties of the catalysts vary very much during the reaction since ethylamine was mainly adsorbed and led to DEA. We suppose that these significant modifications could be due to the polymerisation of reaction intermediates such as imine or enamine. The polymers could remain on the catalyst surface and modify the nature and the number of active sites. In previous works, we remarked that these secondary reactions could modify the catalyst surface (16,17). [Pg.144]

We also examined the adsorption of ethylamine and n-propylamine on the SAPO-5 samples. Again, the results were very similar to those obtained on H-ZSM-5 in that some of the amine desorbed as ammonia and the corresponding olefin between 625 and 700K [4]. Of particular interest was the fact that, for a particular sample, the number of moles which reacted for each amine was the same. This implies that each sample contains a discrete number of acid sites and that each amine samples the same sites. Using this as a measure of the acid site concentration, it is interesting to compare the site concentration to the concentration of substituted metals. This is shown in Table 2 for isopropylamine on the SAPO-5 samples and on MAPO-5(1) and CoAPO-5(1). For this comparison, we used the gel concentration as a measure of the framework metal ion content. [Pg.185]


See other pages where Ethylamine adsorption is mentioned: [Pg.124]    [Pg.303]    [Pg.87]    [Pg.626]    [Pg.226]    [Pg.241]    [Pg.70]    [Pg.97]    [Pg.356]    [Pg.611]    [Pg.611]   
See also in sourсe #XX -- [ Pg.62 , Pg.426 ]




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Ethylamines

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