Solid acid supports

5 Activation of the Metallocenes Cp ZrCl or (BuCp)2ZrCl2 by Solid Acid Supports 

In a novel approach to activate the metallocene compound with a strong Lewis acid supported on a solid support such as silica or alumina, scientists at Chevron-Phillips Chemical Company reported a series of high-activity catalysts suitable for the slurry process [5,7]. This method does not employ an alumoxane compound to activate the catalyst. 

The inorganic supports shown in Table 4.7 were impregnated with various Lewis acids using aqueous solutions following an incipient wetness technique in which the total pore volume of the support was approximately equal to the pore volume of the aqueous solution. Supports were initially dried at 110°C to isolate a free-flowing powder intermediate material [5]. 

The intermediate material was placed into a quartz tube contained in a furnace and a stream of dry air or dry nitrogen was used to fluidize the material in the quartz tube. Then the fluidized material was calcined for several hours at 200-700°C, after which the column was cooled to ambient conditions and the calcined material was stored in an inert atmosphere until needed. 

Support Grade Surface Area (mg) Pore Volume (cc/g) Source 

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Capture of Active Catalyst Using Solid Acidic Support with H2 Elution. The limit on the practical life of a catalyst solution may be determined by several factors including the presence of poisons or inhibitors, the buildup of less soluble materials such as the oxidation products of organophosphorus ligands, or an increase in the concentration of heavy aldehyde condensation products in the catalyst solution. In the latter case, there may be substantial amounts of active catalyst, but it is in a solvent that is unsuitable. Alternately, active rhodium catalyst may have been carried over with product. Technology has been disclosed [39] that permits the isolation of an active metal hydride catalyst. Steps include ... 

Catalyst Reactivation Using Propargyl Acetate. The Wiped-Film Evaporator/02 reactivation procedure and the Capture of Active Catalyst Using Solid Acidic Support with FI2 Elution procedure (see above) both involve the separation of uncomplexed phosphine from rhodium complex. Since the value of the uncomplexed phosphine is significant, technology that does not require separation of phosphine during catalyst reactivation is desirable. 

For the most highly developed processes, maf coal conversion can be as high as 90 to 95 % with a C4+ distillate yield of 60 to 75 wt % and a hydrogen consumption of 5 to 7 wt %. When an external catalyst is used, it is typically some combination of cobalt, nickel, and molybdenum on a solid acid support, such as silica alumina. In slurry hydrogenation processes, catalyst life is typically fairly short because of the large number of potential catalyst poisons present in the system. 

A mixture of phenol 1 (10 mmol) and a,/ -unsaturated carboxylic derivative 2, 4 or ethyl acetoacetate 6 (15-20 mmol) supported on 1 g of solid acid support (by dissolving the mixture in 5 mL of diethyl ether followed by evaporation of the solvent) was exposed to microwave irradiation in a focused microwave reactor (Prolabo MX350). For isolation of the compounds, the solid support was removed by extraction with ethanol (for reactants 2 and 6) or acetonitrile (reactions of 4). After solvent evaporation, the products were purified by column chromatography on silica gel (hexane-ethyl acetate, 3 1). 

Reactions Catalysed by Solid Acid Supported Reagents... 

Patents and literature reviews reveal that a wide range of catalysts has been investigated for the production of pyridine bases [5,9-11,14-18]. Up to 1980, FCC-based catalysts, often in combination with metal promoters, featured heavily as supports. The list of early solid-acid supports includes AI2O3, clays (e. g. mont-morillonite), amorphous Si02-Al203, molecular sieves (i. e. LTA), zeolites MOR and FAU (i. e. H -Y) [19], and metal phosphates [20]. 

Suzuki, T. and Suga, Y. 1997. Solid acid supported metallocene catalysts for olefin polymerization. Polymer Preprints 38 207-208. 

Table 4.7 Supports investigated for activation of metallocenes by solid acid supports.

Activation of Bridged Metallocenes by Solid Acid Supports... 

In an important follow-up study to the activation of the non-bridged metallocene compounds by solid add supports discussed above, scientists at Chevron-Phillips Chemical Company reported [7] the activation of bridged metallocenes, designated as ansa-metallocenes, using the same solid acid supports investigated above [5]. 

The activation of certain ansa-metallocenes to solid acid supports produces polyethylene with relatively low levels of long-chain branching, which is sufficient to moderately increase the molecular weight distribution of the polyethylene, and improve the polymer processability, but not be detrimental to the properties of the finished fabricated product. Consequently, low levels of LCB improve the shear-thinning behavior of the molten polyethylene, which resolves the processing disadvantage of polyethylene with a polydispersity index of 2. 

Polyethylene products produced with the Phillips loop process using catalysts prepared with metallocene compounds activated with solid acid supports are available commercially. 

Recently, a non-covalently supported iminium-type primary amine catalyst 181 has also been developed using polyoxametalate as the solid acid support (Scheme 5.52) [80]. The catalyst was applied to asymmetric Diels-Alder reactions of a-substituted acroleins with good activity and stereoselectivity and could be recycled and reused for six runs. 

Many superacid-catalyzed reactions were found to be carried out advantageously not only using liquid superacids but also over solid superacids, including Nafion-H or certain zeolites. We extensively studied the catalytic activity of Nafion-H and related solid acid catalysts (including supported perfluorooctanesulfonic acid and its higher ho-... 

Slotted plate for catalyst support designed with openings for vapor flow Ion exchanger fibers (reinforced ion exchange polymer) used as solid-acid catalyst None specified Hydrolysis of methyl acetate Evans and Stark, Eiir. Pat. Appl. EP 571,163 (1993) Hirata et al., Jap. Patent 05,212,290 (1993)... 

The synthesis of imidazoles is another reaction where the assistance of microwaves has been intensely investigated. Apart from the first synthesis described since 1995 [40-42], recently a combinatorial synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles has been described on inorganic solid support imder solvent-free conditions [43]. Different aldehydes and 1,2 dicarbonyl compounds 42 (mainly benzil and analogues) were reacted in the presence of ammonium acetate to give the trisubstituted ring 43. When a primary amine was added to the mixture, the tetrasubstituted imidazoles were obtained (Scheme 13). The reaction was done by adsorption of the reagent on a solid support, such as silica gel, alumina, montmorillonite KIO, bentonite or alumina followed by microwave irradiation for 20 min in an open vial (multimode reactor). The authors observed that when a non-acid support was used, addition of acetic acid was necessary to obtain good yields of the products. 

Zeolites have ordered micropores smaller than 2nm in diameter and are widely used as catalysts and supports in many practical reactions. Some zeolites have solid acidity and show shape-selectivity, which gives crucial effects in the processes of oil refining and petrochemistry. Metal nanoclusters and complexes can be synthesized in zeolites by the ship-in-a-bottle technique (Figure 1) [1,2], and the composite materials have also been applied to catalytic reactions. However, the decline of catalytic activity was often observed due to the diffusion-limitation of substrates or products in the micropores of zeolites. To overcome this drawback, newly developed mesoporous silicas such as FSM-16 [3,4], MCM-41 [5], and SBA-15 [6] have been used as catalyst supports, because they have large pores (2-10 nm) and high surface area (500-1000 m g ) [7,8]. The internal surface of the channels accounts for more than 90% of the surface area of mesoporous silicas. With the help of the new incredible materials, template synthesis of metal nanoclusters inside mesoporous channels is achieved and the nanoclusters give stupendous performances in various applications [9]. In this chapter, nanoclusters include nanoparticles and nanowires, and we focus on the synthesis and catalytic application of noble-metal nanoclusters in mesoporous silicas. 

A variety of reactions have been conducted. Catalysts based on noble metals on Deloxan amino poly siloxane supports have been used. Hitzler et al. (1998) have reported alkylation of mesitylene with propylene or wopropanol in SC propylene or CO2 using a solid acid Deloxan catalyst. Pesiri et al. (1998) have carried out selective epoxidation in SC CO2 with transition metal catalysts (V, Ti, Mo) and tert-BHPO high conversion and selectivity have been reported. 

Other hydroxylic solid-phase supports such as cross-linked agarose are similarly activated with CDI or V V -carbonyldi-1,2,4-triazole. The activated matrices can then be smoothly coupled with AT-nucleophiles such as glycine, 6-aminohexanoic acid, diamines, or proteins. 212 ... 

Reactivity of a number of solid acid catalysts that include zeolites, resin, nafion and HP As was determined for the direct reaction of ethylene with acetic acid to produce ethyl acetate (Table 1). It was established that the Keggin HSiW supported on silica is very active for the vapom phase reaction of acetic acid with ethylene at about 180°C, 145 psig with a high molar ratio of ethylene to... 

In summary, the Avada process is an excellent example of process intensification to achieve higher energy efficiency and reduction of waste streams due to the use of a solid acid catalyst. The successful application of supported HP As for the production of ethyl acetate paves the way for future applications of supported HP As in new green processes for the production of other chemicals, fuels and lubricants. Our results also show that application of characterization techniques enables a better understanding of the effects of process parameters on reactivity and the eventual rational design of more active catalysts. 

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