Montmorillonite active sites

Circulation flow system, measurement of reaction rate, 28 175-178 Clausius-Clapeyron equation, 38 171 Clay see also specific types color tests, 27 101 compensation behavior, 26 304-307 minerals, ship-in-bottle synthesis, metal clusters, 38 368-379 organic syntheses on, 38 264-279 active sites on montmorillonite for aldol reaction, 38 268-269 aldol condensation of enolsilanes with aldehydes and acetals, 38 265-273 Al-Mont acid strength, 38 270-271, 273 comparison of catalysis between Al-Mont and trifluorometfaanesulfonic acid, 38 269-270... 

The high dehydrogenation activity observed for Cr3 sa-montmorillonite almost certainly arises from the facile accessibility of the chromium oxide aggregates supported in the clay gallery. Substantial contribution to the observed activity due to active sites at the external surfaces of the mineral is precluded by the virtual absence of activity for the Cr1 88 derivative. Thus, Cr3 53-montmorillonite behaves catalytically much like bulk chromium oxide supported on alumina (17) ... 

Amount of Active Sites on Montmorillonite for Aldol Reaction... 

Adsorption and separation processes involve also the active sites existing on the external surface of (CH3)4N - montmorillonite, their role being more important in the case of adsorption of isoparaffins and cyclohexane molecules. This is indicated by a significantly smaller differences between the specific retention volumes of iso- and cycloparaffins on natural and tetramethylammonium samples than the difference in Vm values characteristic for n-paraffines on the same adsorbents. Thus, the tetramethylammonium montmorillonite adsorbs n-alkanes selectively from the mixtures containing iso- and cycloparaffines, which is confirmed by the values of relative retention volumes for such hydrocarbon pairs as, for instance, n-heptane / 2,4- dimethylpentane. These can be easily calculated from the data presented in Table 5. 

The decrease of Vm and Ki values for the adsorption of benzene on the cetylpyridi-nium montmorillonite prepared from the heated Li-form (samples 5, 6) relative to the modified material based on initial Li-montmorillonite (sample 7) can be explained by the closing of the interlayer gaps of the thermoprocessed mineral. This prevents most active sites of the external surface, the micropores on side faces, from taking part in the adsorption-separation processes. 

Pd-hexadecylammonium montmorillonite (Pd-HDAM) catalysts have been prepared by a novel synthetic route. Sample characterization including XRD and TEM measurements confirmed the existence of interlayer Pd nanocrystallites which occupy clay particle defect sites. The catalytic activities of Pd-HDAM samples were tested by hydrogenation of 1-octene and styrene in the liquid phase. The reaction of styrene was found to be less dependent on the dispersion of Pd than that of 1-octene. The highest activities were observed for samples of low and medium Pd content. The application of various solvents made it pos le to establish a correlation between the activities and the basal spacings dL of Pd-HDAM samples. When the value of dL exceeded 3 ran, interlamellar active sites became more accessible for reactants. 

The catalytic application of montmorillonites may either be related to their acidity [5-7], or their swelling properties [8-9], Swelling, induced by careful selection of both the reaction medium and interlayer cations, enables the reactant molecules to enter the interlamellar region and undergo catalytic reaction on interstitial active sites. Moreover, the layered structure of montmorillonite may induce a substrate selectivity depending on the reactant size. Therefore, clay intercalated metal catalysts offer potential applications in the preparation of fine chemicals. 

For silica, 6g is the same for aqueous solutions (in distilled water) and for alkaline solutions (Table I), but is different from that of glass. The areas per active site =SiOX are, respectively, 52.5 and 65 sq.A. at the surface of glass and silica. These values are close to the values given by Brooks for sodium and calcium montmorillonites and for aerosil [5, 6]. 

The surface excess isotherms for methanol adsorption from benzene on untreated montmorillonites and kaolinite were both of type II in the Schay classification. " Pretreatment of montmorillonite with water+isopropanol or with methanol (50 h contact with boiling liquid) lowered the initial part of the isotherm indicating that pretreatment had covered some of the more active sites, but the final slope as x (alcohol) 1 was unchanged showing that the... 

The authors [2] studied the kinetics of poly (amic acid) (PAA) solid-state imidization in nanofiller (Na -montmorillonite) presence and foimd an essential reaction acceleration both at imidization temperature raising in the range 423-523 K and Na" -montmorillonite contens increase within range 0-7 phr. The possible chemical mechanism of Na" -montmorillonite action as a catalyst was offered, assuming larger contact surface area and respectively larger number of reaction active sites, that promotes dehydration and imide ring closure reaction [2]. This model has hypothetical and qualitative character. However, it became obvious lately, that on chemical reac-... 

Active sites on montmorillonite lamellae Results Literature... 

Composites can be formed between phosphazenes and other dissimilar materials. Nanohybrids of a funetionalized phosphazene and montmorillonite clay. ° The phosphazene was a cyclic trimer substituted with a poly[ethylene-propylene] ehain, Seheme 34. The pendant group was prepared and substitution was faeilitated by K2CO3 as the base. Prior to the phosphazene intercalation, the montmorillonite was treated with base to activate sites for bonding to occur with the phosphazene. 

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