Immobilization on Alumina

An alumina matrix may be prepared with high pore density (more than 60 %) and pore diameters ranging from 5 to 250 nm. Ruiz-Hitzky et al. [214] immobilized GOD in nanoporous alumina membranes with regular hexagonal arrays of highly ordered cylindrical pores aligned perpendicularly to the membrane surface. GOD was anchored in the membrane by the highly hydrophilic chitosan biopolymer. Full activity was maintained for at least 50 hours. 

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Numerous examples of solid/solid/liquid phase transfer catalysis are now known to be useful synthetically but have not been investigated mechanistically. Poly(ethylene glycol) immobilized on alumina and silica gel is active for reaction of solid potassium acetate with 1-bromobutane 184). Some of the best synthetic results with polymer supports are shown in Table 15. Often use of other solid salts or other catalysts gave poorer yields. It would be valuable to know for the design of future syntheses how these reactions depend on the partial solubility of the inorganic salts in the organic solvents and on the presence of trace amounts of water. 

Highly dispersed palladium nanoparticles immobilized on alumina were prepared via the sonochemical reduction by alcohols of Pd(II).366 The activity of these catalysts was 3-7 times higher in the hydrogenation of alkenes than that of conventional catalysts, and they showed a high preference to hydrogenate 1-hexene over trans-3-hexene. 

More than half a century ago it was observed that Re207 and Mo or W carbonyls immobilized on alumina or silica could catalyze the metathesis of propylene into ethylene and 2-butene, an equilibrium reaction. The reaction can be driven either way and it is 100% atom efficient. The introduction of metathesis-based industrial processes was considerably faster than the elucidation of the mechanistic fundamentals [103, 104]. Indeed the first process, the Phillips triolefin process (Scheme 5.55) that was used to convert excess propylene into ethylene and 2-butene, was shut down in 1972, one year after Chauvin proposed the mechanism (Scheme 5.54) that earned him the Nobel prize [105]. Starting with a metal carbene species as active catalyst a metallocyclobutane has to be formed. The Fischer-type metal carbenes known at the time did not catalyze the metathesis reaction but further evidence supporting the Chauvin mechanism was published. Once the Schrock-type metal carbenes became known this changed. In 1980 Schrock and coworkers reported tungsten carbene complexes... 

The limitations of standard reversed-phase materials have been partially overcome by introducing modem, specially deactivated hydrocarbon-silica pha.ses ]126]. the hydrocarbonaceous phases immobilized on alumina or zirconia support ]127] and the polymeric materials ]128]. Using the latter two types of stationary phase materials one can determine the HPLC capacity factors at acidic, neutral and alkaline conditions. This way a universal, continuous chromatographic hydrophobicity scale can be constructed like the standard log P scale ] 129]. 

Stability of Bromate Speeies Immobilized on Alumina Microcolumns Interlaboratory Exercise for Bromate Determination... 

Stability of Bromate Species Immobilized on Alumina Microcolumns... 

Oxidative homocoupling of 4-hydroxy-3-methoxyphenylacetic acid using H2O2 is achieved using a miniaturized reactor having peroxidase immobilized on alumina surfaces to give 2,2 -dihydroxy-3,3 -dimethoxybiphenyl-5,5 -diacetic acid (Figure 7.14) [74]. 

Glycoside-decorated amino-ether dendrons of up to third generation were prepared in solution and subsequently covalently immobilized on alumina chip by Pieters, Liskamp, and coworkers.The study of the binding of fluorescence-tagged lectins to the glycoclusters on the chip revealed the multivalency enhancement of the binding. 

Onium salts immobilized on alumina have been shown to be effective phase-transfer catalysts in comparison to analogous soluble catalysts adsorbed on silica or alumina. Thus, 1-bromo-octane with cyanide ion yields nonanenitrile in 90% yield. ... 

FIGURE 4 Activity of glucose-6-phosphate dehydrogenase as a function of time for ( ) the enzyme immobilized on the polyphosphazene/ alumina support and (o) in the presence of free enzyme and non-activated support. (From Ref. 23.)... 

In this work, various Ru-BINAP catalysts immobilized on the phosphotungstic acid(PTA) modified alumina were prepared and the effects of the reaction variables (temperature, H2 pressure, solvent and content of triethylamine) on the catalytic performance of the prepared catalysts were investigated in the asymmetric hydrogenation of dimethyl itaconate (DMIT). 

Fig. 1. P MAS NMR spectrum of (a)Ru-BrNAP/PTA/y-Al203, and (b)Ru-BINAP crt rlex In order to find the characteristics of the immobilized catalyst, asymmetric hydrogenation of the prochiral C=C bond was performed as a model reaction. Firstly, three different homogeneous Ru-BINAP complexes including [RuCl2((R)-BINAP)], [RuCl((R)-BINAP)(p-cymene)]Cl and [RuCl((R)-BINAP)(Benzene)]Cl were immobilized on the PTA-modified alumina. Reaction test of immobilized catalysts showed that [RuCl2((R)-BINAP)] was the most active and selective so all the experiment were done using this catalyst afterwards.

The deployment of chromium(VI) reagents in the oxidative transformation is compromised due to inherent toxicity, involved preparation of its various complex forms (with pyridine or acetic acid) and cumbersome workup procedures. Chromium trioxide (Cr03) immobilized on premoistened alumina enables efficient oxidation of ben -... 

However, with respect to ee, the same catalyst immobilized on amorphous silica performed even better (conversion 72%, ee 92%) than the one immobilized on MCM-41. This example illustrates an important issue, i.e., OMS-based catalysts have to be compared with those based on amorphous silica or silica-alumina. If the amorphous materials perform as well or even better than the OMS materials, then there is no advantage in using the significantly more expensive OMSs. However, in those cases where the catalytic reaction benefits from the regular and well-defined pore systems of the OMS materials, such materials can be very attractive, e.g., for the conversion of bulkier molecules or to overcome transport limitations in more narrow pores. 

Silica-alumina particles coated with a permselective silicalite membrane is almost completely selective in the formation of p-xylene in the disproportionation of toluene.402 Friedel-Crafts alkylations were performed in ionic liquids. The strong polarity and high electrostatic fields of these materials usually bring about enhanced activity.403 404 Easy recycling is an additional benefit. Good characteristics in the alkylation of benzene with dodecene were reported for catalysts immobilized on silica or MCM-41 405... 

Immobilized complexes anchored to the surface of oxide supports may serve as active metathesis catalysts. In fact, Mo(CO)6 on alumina was reported in the first paper on metathesis by Banks and Bailey.1 Molybdenum and tungsten hexacarbo-nyls and alkylmolybdenum and alkyltungsten complexes have been studied most.6,24,26 Anchored organomolybdenum complexes are particularly effective catalysts, even at temperatures below 0°C however, they quickly lose activity.41-43... 

Mena, M.L., A. Morales-Rubio, A.G. Cox, C.W. McLeod, and P. Quevauviller. 1995. Stability of chromium species immobilized on microcolumns of activated alumina. Quim. Anal. 14 164—168. 

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