Montmorillonite, catalytic activity

The performance of clay materials (Halloysite, Pyrophyllite, Montmorillonite K-30) in the degradation of polystyrene (PS) was investigated in this study. The catalysts showed good catalytic activity for the degradation of PS with high selectivity to aromatics liquids. Styrene is the major product, and ethylbenzene is the second most abundant one in the liquid product. 

Montmorillonite K10 was also used for aldol the reaction in water.280 Hydrates of aldehydes such as glyoxylic acid can be used directly. Thermal treatment of K10 increased the catalytic activity. The catalytic activity is attributed to the structural features of K10 and its inherent Bronsted acidity. The aldol reactions of more reactive ketene silyl acetals with reactive aldehydes proceed smoothly in water to afford the corresponding aldol products in good yields (Eq. 8.104).281... 

The intercalated catalysts can often be regarded as biomimetic oxidation catalysts. The intercalation of cationic metal complexes in the interlamellar space of clays often leads to increased catalytic activity and selectivity, due to the limited orientations by which the molecules are forced to accommodate themselves between sheets. The clays have electrostatic fields in their interlayer therefore, the intercalated metal complexes are more positively charged. Such complexes may show different behavior. For example, cationic Rh complexes catalyze the regioselective hydrogenation of carbonyl groups, whereas neutral complexes are not active.149 Cis-Alkenes are hydrogenated preferentially on bipyridyl-Pd(II) acetate intercalated in montmorillonite.150 The same catalyst was also used for the reduction of nitrobenzene.151... 

A biosensor based on mediator-free CYP2B4 catalysis by immobilizing monomer-ized CYP2B4 in montmorillonite was studied by Shumyantseva [222], When substrates were added to air saturated buffer solution, there was an increase in the reduction current. A typical concentration dependence measured in chronamperometry is shown for aminopyrine and benzphetamine (Fig. 17.4). The reaction was inhibited by metyrap-one. This indicates the catalytic activity of CYP2B4 in the presence of substrate. 

Owing to the possibility of tuning (1) their acidic and basic properties, (2) their surface hydrophilicity, and (3) their adsorption and shape-selectivity properties, catalytic activity of zeolites was investigated in the production of HMF from carbohydrates. Whatever the hexose used as starting material, acidic pillared montmorillonites and faujasite were poorly selective towards HMF, yielding levu-linic and formic acids as the main products [81-83]. 

Recently, interest in clays as acidic catalysts has been quickened by the reported high catalytic activity of a synthetic mica-montmorillonite clay and its nickel-containing analogs. Wright et al. (247) have described the structure, thermal modification and surface acidity of the clay, which they designated SMM for synthetic mica-montmorillonite. 

Little or no reactivity is observed for Cri.88" montmorillonite, but the Cr3 53 derivative with a la rge gallery height is much more reactive. Also, it should be noted that, as expected, pure Na+-montmorillonite showed no catalytic activity. The decrease in reactivity with increasing reaction time for Cr3 53-montmorillonite most likely arises from the formation of coke and the concomitant occlusion of gallery pores. 

Bentonite, whose main ingredient is montmorillonite, is one kind of layer structure clay mineral. It is an ideal material for preparation of pillared clays. If metal cations with high catalytic activity were intercalated in the interlayers of montmorillonite, a new type of solid acid catalyst can be obtained. The catalytic activity of the catalyst is closely associated with its porosity, specific surface area and surface total acidity. One of the effective ways to enhance catalytic activity is to prepare catalyst with appropriate metal cations and structure. 

The reaction of 14a with an aldehyde (15b) was also examined with respect to catalytic activity and diastereoselectivity affected both by reaction solvents and by the sort of exchanged cation in the montmorillonite (Table XV, Entries 1-6). Al-Mont showed higher activity than proton- or titanium ion-exchanged montmorillonite (H-Mont and Ti-Mont, respectively) (Entries 1, 2, S, 6). Al-Mont also showed slightly higher diastereoselectivity than H-Mont and Ti-Mont since the reaction proceeded at lower temperature. 

As another example of novel catalysis employing montmorillonite, the clay was found to show excellent catalytic activity for the addition reaction of trimethylsilyl ketene acetal to a, -acetylenic esters (ynoates), which contrasted strikingly with the reactions induced by a homogeneous acid catalyst, trimethylsilyl triflate (TMSOTf), as well as the addition reactions of lithium enolates with ynoates [Eq. (17)] (89). Table XXIII summarizes the results of the reactions of the silicon and lithium enolates of methyl propionate (21) with ynoates (22a-c). Except for the reaction of 22c, ferric ion-exchanged montmorillonite (Fe-Mont), which is more acidic than Al-Mont, catalyzed exclusive 1,2-additions of trimethylsilyl ketene acetal to 22a and 22b to give 23 in... 

There has been renewed interest in catalytically active clays since the report by Swift and Black ( 1) to the effect that replacement of octahedrally coordinated aluminium ions by nickel or cobalt in synthetic smectite clays, as done by Granquist ( ), results in a new type of catalyst, called nickel- (or cobalt-) substituted mica montmorillonite (Ni(Co)SMM), which is very active in the isomerization and cracking of hydrocarbons. 

Among all the acidic supports tested, bentonites or montmorillonites were shown to be especially efficient since 30 minutes in a metallic bath at 350°C are now sufficient in dry media when a 1 2 (w/w) mixture of o-benzoylbenzoic acid with clay is used. The yield is rather similar for both methods but the new process enables a safe and simplified manipulation and treatment (AQ is obtained pure directly by sublimation) [64]. However, some loss in catalytic activity is observed after several reuses of the same clay. It is thought this limitation can be overcome by using microwaves as activation procedure in place of the traditional heating (see below) [65] since within 5 minutes yield is... 

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. 

Several copper-exchanged and CuCl2-supported solids, together with copper oxide, have been tested as catalysts in the benchmark cyclopropanation reaction of styrene with ethyl diazoacetate. The catalytic activity does not depend on the amount of copper but on the structure and pretreatment of the catalyst. The trans/cis selectivity also depends on the nature of the solid and with KlO-montmorillonite the cis-cyclopropane is predominantly obtained, so that the selectivity is reversed with regard to that observed with copper homogeneous catalysts. The use of several olefins confirms this tendency to reverse the selectivity obtained in solution and the electrophilic character of the reaction. The effect of the reaction conditions and the influence of the solvent are also analyzed. 

Catalytic activity depends more on the nature and pre-treatment of the catalyst than on the content of copper. Thus, Cu(II)-exchanged KlO-montmorillonite displays an activity similar to the other clays and CuCl2-supported catalysts in spite of the very low amount of copper contained in that clay. Zeolite Y is less active than clays and does not promote the reaction at room temperature. Finally, calcination under dry air reduces the catalytic activity. 

Figure 5. A comparison of catalytic activities using a light cycle oil over deactivated catalysts based on pillared montmorillonite, pillared rectorite, NaY and an amorphous silica-alumina FCC.

A sample of montmorillonite was pillared with aluminium polyoxycations in presence of different amounts of tween-80, a nonionic surfactant, ranging from 0.01 to 0.20 mmol/meq of clay. The amount of aluminium sorbed was found to vary with the amount of surfactant added during pillaring. Vapour phase catalytic activity of the samples for alkylation of toluene with methanol in a fixed bed down flow reactor showed that the rate of deactivation, in general, increased with decrease in the pillar density. The samples treated with 0.06 to 0.08 mmol/meq of surfactant showed the lowest deactivation and also an enhancement in the mesopores which did not change on calcining to 540 C. Suppression of deactivation is attributed to the distribution of pillars by the surfactant in such a way as to decrease the coke formation. 

Montmorillonite is a layered smectite clay. Acid activation replaces the interlamellar cations with protons, leaches Al from octahedral layers resulting in increase of surface area, porosity and acidity. Clay is activated with a mineral acid for different time intervals. They are characterised by XRD, surface area and acidity by stepwise temperature desorption of ammonia Catalytic activity is studied on aniline alkylation reaction. 

Fig. 3 describes the dependence of aniline alkylation on surface area of the catalysts. Na montmorillonite is inactive for the reaction. Aniline alkylation activity reached a maximum when the surface area of the catalyst is about 130 m g Beyond this, the effect of increase in surface area on the catalytic activity is not conspicuous. Total acidity in the range 40 - 70 X 10 mmole NHsg seems to be favourable for the reaction (fig.4). 

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