Immobilization oxide supports

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... 

A more widely used method of heterogenization has also been applied to MTO, by using a metal oxide support onto which the MTO is applied. MTO has been applied onto niobia (Nb2Os) both via impregnation and sublimation [39] and onto silica (Si02) via reaction of a bipyridine-containing siloxane [40]. In a similar manner, MTO has been immobilized on the mesoporous silica MCM-41 [41]. Zeolite NaY has been used as a support material by the in situ immobilization of the MTO catalyst [42]. 

Three papers have appeared in the past two years on catalysts that are either supported on polymers or are heterogeneous. Djakovitch first reported animation reactions catalyzed by palladium particles immobilized on metal oxide supports, as well as by palladium complexes contained in NaY zeolites [172]. In most cases, these reactions were conducted at high temperatures, generally 135 °C. When NaOtBu was used as the base, competing amination through a benzyne intermediate was observed. Thus, para meta regioselectivity was not high, and reaction yields were modest. 

Alternatively, surface-mediated synthesis involves the immobilization of a mononuclear metal complex (similar to the ones described in Sect. 19.2) and the subsequent treatment in CO at different temperatures to form a supported metal carbonyl cluster, for example, [HIr (CO)jJ formed from Ir(CO)2(acac) on MgO and [Rhj(CO),5] formed from Rh(CO)2(acac) on MgO and y-Al Oj [45 7]. Synthesis of metal carbonyl clusters on oxide supports apparently often involves OH groups or water on the support surface analogous chemistry occurs in solution [13]. The synthesis of molecular catalysts from a mononuclear metal complex is likely to occur with a yield less than that associated with simple adsorption of a preformed metal cluster, and so the latter precursors are preferred, except when they do not fit into the pores of the support (e.g., a zeolite). 

A special feature of photoimmobilized systems is their ability to catalyse the reaction in unexpected direction as compared to immobilized and supported catalysts of the same chemical nature. Two new catalytic reactions, proceeding over the photoimmobilized catalysts at a low temperature, have been discovered. One of them is the n-butane oxidation to ethene oxide over... 

Galactosidase has been attached to glass in this way.56 The immobilized enzyme is useful in removing lactose from milk, for the benefit of those persons who are intolerant of lactose. A similar technique was used to attach glucose oxidase to magnetite (I i O-i) particles, starting with a trimethoxysilane.57 This permits easy separation with a magnet. The immobilized enzyme was 50% less active than the native enzyme, but kept 95% of its activity after 9 months at 4°C. Another way to attach an enzyme to a support is to treat the metal oxide support first with 2,4,6-trichloro 1,3,5 triazine (cyanuric chloride) (5.18), then with the enzyme.58 This was done on both alumina and on silica. 

The triblock poly(alkene oxide)-supported catalysts 88 and 90 can be simply prepared using the same chemistry used earlier to prepare poly(ethylene oxide)-immobilized hydrogenation catalysts (Eqs. 29 and 30) [124]. Once prepared, these ligands and their Rh(I) complexes separate as oil-in-water emulsions from water at temperatures in the 0-50 °C range. The actual LCST depends on the substrate concentration and on the ratio of hydrophilic/hy-... 

The most general observation is to be made on the basis of the tracer studies that only a part of surface sulfur is mobile or exchangeable on catalysts with sulfides and oxides. Supported Co and Ni contain only mobile sulfur, if sulfided by thiophene and contain both mobile and immobile sulfur, if they are sulfided by H2S/H2.[ 1 This is interpreted with the differences in the metal-sulfur bond strengths, as the edge S-atoms are held more weakly than the top S-atoms of the slab.I This follows from the results of some radiosulfur tracer studies of metal single crystals that different surface S-species are formed at different surface sulfur concentrations, and on different crystal faces of Pt, and... 

Oxidation reaction of glucose is achieved with microfluidic channels fabricated from poly(dimethylsiloxane) (PDMS) using immobilized microbead-supported... 

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