Alcohols adsorption experiments

However, the true particular sites of aluminas for most catalytic reactions are very likely the anion-cation couples, which have very high activity and work syner-gistically. Alcohol adsorption experiments [127,164] allow the characterization of such sites where dissociative adsorption occurs. Mechanistic studies suggest that such cation-anion couples are likely those active in alcohol dehydration [165], in alkylchloride dehydrochlorination [152,166], and in double bond isomerization of olefins [167] over y-Al203. 

Co-adsorption experiments show a complex role of the nature and concentration of chemisorbed ammonia species. Ammonia is not only one of the reactants for the synthesis of acrylonitrile, but also reaction with Br()>nsted sites inhibits their reactivity. In particular, IR experiments show that two pathways of reaction are possible from chemisorbed propylene (i) to acetone via isopropoxylate intermediate or (ii) to acrolein via allyl alcoholate intermediate. The first reaction occurs preferentially at lower temperatures and in the presence of hydroxyl groups. When their reactivity is blocked by the faster reaction with ammonia, the second pathway of reaction becomes preferential. The first pathway of reaction is responsible for a degradative pathway, because acetone further transform to an acetate species with carbon chain breakage. Ammonia as NH4 reacts faster with acrylate species (formed by transformation of the acrolein intermediate) to give an acrylamide intermediate. At higher temperatures the amide may be transformed to acrylonitrile, but when Brreform ammonia and free, weakly bonded, acrylic acid. The latter easily decarboxylate forming carbon oxides. 

It is also observed in Fig. 5.3 that Pd(II) ions are partly adsorbed on AI2O3 before ultrasonic irradiation the concentration of Pd(II) just before irradiation becomes ca. 0.8 mM, although 1 mM Pd(II) was added in the sample solution. From a preliminary adsorption experiment, the rate of Pd(II) adsorption on A1203 was found to be slow compared with those of Pd(II) reduction in the presence of alcohols. Therefore, it is suggested that the sonochemical reduction of Pd(II) in the presence of alcohols mainly proceeds in the bulk solution. The mechanism of the Pd/Al203 formation is also described in the section of sonochemical synthesis of supported metal nanoparticles. 

The residuals discussed thus far have been associated with some dependent variable, such as the reaction rate r. It is particularly advantageous in pinpointing the type of defect present in an inadequate model to expand this definition to include parametric residuals. The parametric residual, then, is simply the difference between a value of a given parameter estimated from the data and that predicted from a model. For example, the dots in Fig. 17 represent the logarithm of the alcohol adsorption constants measured in alcohol dehydrogenation experiments from isothermal data at each of several temperature levels (FI). The solid line represents the expectation that these... 

To assess the effect of an adsorbed layer of polyvinyl alcohol on the rate of polymerisation, the rates of seeded polymerisation were measured after adsorption of various grades of polyvinyl ailcohol on the seed latex. The seed latex was prepared in the same way as the latex used in the adsorption experiments. After adsorption of polyvinyl alcohol from a 0.10 % w/v solution, the concentration of the seed latex wets 0.9A5 % w/v in a 2.0 % v/v vinyl acetate solution containing 7.4 x 10" mol dm" potassium persulphate. The rates of polymerisation (the means of two to four experiments) observed at 60 C are tabulated below. 

The cell shown in Fig. 7 has been designed to be placed outside the sample compartment of the spectrometer. It has the advantage of requiring only a small volume of electrolyte (c. 5 ml). The solution can be replaced while the working electrode is kept under potential control. This can be very useful in adsorption experiments with organic fuels, as we shall see in the sections devoted to adsorption of alcohols. 

As for the chemisorption of the molecule of prenal results from adsorption experiments suggest than, at least two adsorption states can exist on the surface. Besides, the time course of the reaction (fig. 2)s showing saturated alcohol at the very beginning of the reaction, suggests that under standard conditions, the molecule can be adsorbed flat on the surface. In this configuration, both the C=C and the C=0 bonds are activated, and there is no clear preferential hydrogenation of the one or the other (equivalent proportions of prenol and isovaleraldchydc). 

It should be noted that the adsorption experiment described above involves systems that only contain surfactant, cosurfactant, brine and reservoir rock. There is no oil present in the system, and this is the reason why the ratio of cosurfactant to surfactant is higher than usually reported by other researchers. It was found that the higher ratio was necessary for complete dissolution of surfactants in the brine since a lower alcohol/surfactant ratio caused the solutions to become cloudy. This latter condition resulted in substantial increases in surfactant retention in flow experiments. The observation of the relationship between the solution condition and retention lead to experiments which could better define the phenomenon. 

A theoretical analysis of these experiments is presented by Dekany, Nagy, and Schay and by Dekany and Nagy. In their presentations the assumptions involved are not all stated explicitly, and some of these seem to be mutually incompatible. The following somewhat more complete argument is suggested, which brings out these points more clearly. First it is assumed, with the authors, that the molecules are the same size and that the ratio of the surface activity coefficients can be taken as unity. If adsorption occurs independently on the two types of site A, B, with adsorption equilibrium constants for alcohol adsorption Xa and Kb, respectively, then the surface mole fractions of alcohol on the two types of site are... 

The research on VOC adsorption in MOFs is still at its early stage. Experimental studies can only be found on alkane and alcohol adsorption in MOFs. The adsorption of some critical VOCs, such as benzene and formaldehyde, has been studied with molecular simulation or theoretical calculation. Therefore, experimental investigation of the removal of VOCs with MOFs as novel adsorbents, especially VOCs with higher threat to environmental and human health, is urgently needed. An experiment and simulation combinatorial screening study will be important to start the exploration of MOFs for the removal of VOCs. 

The different rate of adsorption in aqueous and alcoholic solution can be demonstrated by a simple experiment. Charcoal in sufficient amount is shaken with a dilute aqueous solution of crystal violet and renders the solution practically colourless. If the latter is now replaced by an equal volume of alcohol,... 

Similar conclusions may be drawn from the experiments of Hardy on lubrication. Hardy has obtained very convincing data in support of the hypothesis that on the adsorption of a vapour such as octyl alcohol by a metal surface, whilst the first layer is held very tenaciously the thickness of the film of vapour condensed on the metal surface which is in equiUbrium with the free surfeice of the liquid is certainly multimolecular in character and those layers forming the secondary film may be squeezed out by application of sufficient pressure. 

Most liquid chromatographic experiments performed with PAD employ alkaline mobile phases or use postcolumn addition of base to get the electrode at the appropriate pH for the formation of the oxide. The exceptions to this are the detection of carbohydrates and alcohols in acidic media and the detection of sulfur compounds. The oxidation of carbohydrates and alcohols is not oxide catalyzed, and since they exhibit a stronger adsorption to piatinum than gold, they can be determined under acidic conditions. Sulfur compounds are adsorbed at oxide-free surfaces, and the kinetics for detection are favorable even at pH values below 7. 

Alcohols also promote wettability and penetration of the wood surface. This may easily be shown by the following simple experiment. When equal sized drops of distilled water were placed on the surface of a freshly planed piece of southern yellow pine, the times for the drops to completely soak into the wood were observed. On the early wood it took 65 seconds and on the latewood 179 seconds. When similar drops of 50% ethanol solution were used instead of pure water, it required only six seconds to disappear into the earlywood and 26 seconds into the latewood. However, if a small drop of adhesive syrup, with no hardener added, was placed on the wood surface, no adsorption took place at all. It was surmised that the viscosity prevented its permeation. When the adhesive was diluted with 50% alcohol it was readily absorbed and produced a red stained spot on either earlywood or latewood areas. This showed that the low molecular weight adhesive molecules could readily permeate the wood structure before condensation with the curing agent. 

One possible explanation for the broad mle = 44 feature may be found in the thermal decomposition of a lithium alkyl carbonate produced by the reaction between PC and Li, for which C02 would be released at a much lower temperature than the corresponding inorganic carbonate. The formation of such a species has been suggested by Aurbach and co-workers on the basis of in situ and ex situ external reflection FTIR measurements performed in PC-based electrolytes [18]. Support for this assignment was obtained from experiments in which a genuine alkyl carbonate was prepared in UHV by exposing to C02 a layer of lithium alkoxide formed by the adsorption of an alcohol onto the Li surface, as described in Section I.E. 

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