Silicic acid catalyst

The hydroamination of alkenes has been performed in the presence of heterogeneous acidic catalysts such as zeolites, amorphous aluminosilicates, phosphates, mesoporous oxides, pillared interlayered clays (PILCs), amorphous oxides, acid-treated sheet silicates or NafioN-H resins. They can be used either under batch conditions or in continuous operation at high temperature (above 200°C) under high pressure (above 100 bar). 

Some non-silica sol-gel materials have also been developed to immobilize bioactive molecules for the construction of biosensors and to synthesize new catalysts for the functional devices. Liu et al. [33] proved that alumina sol-gel was a suitable matrix to improve the immobilization of tyrosinase for detection of trace phenols. Titania is another kind of non-silica material easily obtained from the sol-gel process [34, 35], Luckarift et al. [36] introduced a new method for enzyme immobilization in a bio-mimetic silica support. In this biosilicification process precipitation was catalyzed by the R5 peptide, the repeat unit of the silaffin, which was identified from the diatom Cylindrotheca fusiformis. During the enzyme immobilization in biosilicification the reaction mixture consisted of silicic acid (hydrolyzed tetramethyl orthosilicate) and R5 peptide and enzyme. In the process of precipitation the reaction enzyme was entrapped and nm-sized biosilica-immobilized spheres were formed. Carturan et al. [11] developed a biosil method for the encapsulation of plant and animal cells. 

The silica carrier of a sulphuric acid catalyst, which has a relatively low surface area, serves as an inert support for the melt. It must be chemically resistant to the very corrosive pyrosulphate melt and the pore structure of the carrier should be designed for optimum melt distribution and minimum pore diffusion restriction. Diatomaceous earth or synthetic silica may be used as the silica raw material for carrier production. The diatomaceous earth, which is also referred to as diatomite or kieselguhr, is a siliceous, sedimentary rock consisting principally of the fossilised skeletal remains of the diatom, which is a unicellular aquatic plant related to the algae. The supports made from diatomaceous earth, which may be pretreated by calcination or flux-calcination, exhibit bimodal pore size distributions due to the microstructure of the skeletons, cf. Fig. 5. 

We have also investigated the properties of several of our nanostructured catalysts as solid acids in reactions such as the dehydration of alcohols and transesterification reactions [99]. One of the best examples of atomically dispersed solid acid catalysts is aluminosilicates [100]. When aluminium is substituted into silicate frameworks and remains isolated from other A1 centers it can behave as a strong acid site [101]. 

A. This distance is the distance between the hydrogen on the first carbon and the third carbon atom in an aliphatic chain. This critical condition of the catalyst is satisfied by sulfuric acid, phosphoric acid, silicic acid, aluminosilicic acid, perchloric acid, moist aluminum chloride ( HAICI4 ), and partially hydrogenated nickel. 

Assuming that condensation involves only the participation of silicic acid (the monomer), then under conditions of constant water and catalyst concentrations, the resulting rate expressions are (29) ... 

The way in which the proton is associated with the alumina-silica catalyst is a matter of some doubt. Thomas (78) assumes the aluminium to be tetrahedral when linked with tetrahedral silicon, the extra valence electron being supplied by hydrogen from water contained in the catalyst (Fig. 21a). Both aluminium hydroxide and silicic acid are very weak acids because of the affinity of oxygen for the hydrogen (83), and a coordination of aluminium with the hydroxyl oxygen contained in the catalysts... 

Montmorillonite clays are layered silicates montmorillonite K-10 is a specially manufactured acidic catalyst (Montmorillonite K10, [1318-93-0] A. Comelis, P. Laszlo, M. W. Zettler in eEROS Encyclopedia of Reagents for Organic Synthesis, L. A. Paquette, Ed., John Wiley and Sons, Inc., online reference available at http //www.intersciene.wiley.com)... 

The ether extract containing the catalyst and neutral products was fractionally distilled (130°-160°C at 0.01 mm Hg). The soluble catalyst was concentrated in the pot residues. The distillation fractions were then chromatographed through a silicic acid column. Monoesters and cyclic ketones were eluted successively with 5 95 and 10 90 diethyl ether petroleum ether, and more polar material was eluted with 15 85 diethyl ether. -petroleum ether followed by pure diethyl ether. 

The silicic acid used for column chromatography and the Amberlite resin were Silicar CC-7 100-200 mesh purchased from Mallinckrodt Chemical Works, St. Louis, Mo. The 5% palladium on charcoal catalyst was purchased from Engelhard Industries Ltd., Newark, N. J. The tri-O-acetyl-D-glucal and the tri-O-acetyl-D-galactal (as a 70% solution in benzene) were purchased from Raylo Chemicals Limited, Edmonton, Alberta. 

Hydration of Ethyl Ether. Using the same type of acid catalysts as in the hydration of ethylene to ethanol, ethyl ether can be hydrated to the alcohol. Catalysts that have been used for the hydration of ether include phosphoric acid (144), sulfuric acid (145,146), hydrochloric acid (147), metallic oxides (141,148,149) and silicates (150). Sulfuric acid concentrations ranging from 5-25% at 200°C (144) to 63-70% at 110-135°C and 1.01-1.42 MPa (10—14 atm) (148) have been claimed. 

The alkylation of benzene is the most important reaction in the further use of this compound (Table 4, entry 29) [1]. The reaction is performed in the liquid phase with Friedel-Crafts catalysts or in the gas phase with acid catalysts such as H3PO4, aluminum silicates, or BF3. More than 50% of benzene consumption... 

Segmented gas-liquid (Taylor) flow was used for particle synthesis within the liquid slugs. Tetraethylorthosilicate in ethanol was hydrolyzed by a solution of ammonia, water and ethanol (Stober synthesis) [329]. The resulting silicic acid monomer Si (OH)4 is then converted by polycondensation to colloidal monodisperse silica nanoparticles. These particles have industrial application, for example, in pigments, catalysts, sensors, health care, antireflective coatings and chromatography. 

In the case of the VPO catalyst for the butane oxidation process and the MCM catalyst for the acrylonitrile process, the preferred precursor of the peripheral hard phase is polysilicic acid (PSA). The term "polysilicic acid" is generally reserved for those "silicic acids that have been formed and partially polymerized in the pH range 1-4 and consist of ultimate silica particles generally smaller than 3-4 nm diameter" (4). Small, discrete particles of colloidal silica also migrate to the periphery of the droplet, but they do not coalesce as extensively as PSA in drying. The larger the particle size, the lower the mechanical strength of the coalesced dry product. 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert silica or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acrylic acid were prepared from bismuth, cobalt, iron, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic silicic acids. Preferred second-stage catatysts generally7 are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity7 and productivity7 (39,45,46). 

Protonic zeolites find industrial applications as acid catalysts in several hydrocarbon conversion reactions. The excellent activity of these materials is due to two main properties a strong Bronsted acidity of bridging Si—(OH)-Al sites (Scheme 3.4, right) generated by the presence of aluminum inside the silicate framework and shape selectivity effects due to the molecular sieving properties associated with the well defined crystal pore sizes, where at least some of the catalytically active sites are located. 

The catalysts preparable with swelling layer lattice silicates are classified into four types, as illustrated in Fig. 1. The intercalate of hydrated metal ion (a. Fig. 1) is easily obtained by a simple ion-exchange reaction in an aqueous medium. The intercalate acts as a Br0nsted acid catalyst because... 

A survey of the reactions of methanol and butene over a series of M" -TSMs leads us to note two common features. First, no activity is observed with some M" -TSMs, indicating that the silicate sheet of TSM is catalyti-cally inactive. Second, M" -TSM does not follow the clear activity sequence that is frequently noted in acid catalysts, of which the surface acidity is changed by the inductive effect of metal ions (27, 22). These features strongly suggest that the direct interaction between a substrate and the interlayer metal ion is responsible for the catalysis by M" -TSM, namely, M"" -TSM acts as an immobilized metal ion catalyst. 

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