Aluminium chloride, silica-supporte

The product distribution in the reaction of benzene with dodecene was determined for a number of catalysts (Table 5.1-4). As can be seen, the reaction with the zeolite H-Beta gave predominantly the 2-phenyldodecane, whereas the reaction in the pure ionic liquid gave a mixture of isomers, with selectivity similar to that of aluminium chloride. The two supported ionic liquid reactions (H-Beta / IL and T 350 / IL) again gave product distributions similar to aluminium(III) chloride (T350 is a silica support made by Degussa). 

Bound reagents are an excellent alternative in cases where the reagent is used in excess and can be difficult to remove. Purification is now a simple process of filtration and evaporation. For example, silica-supported aluminium chloride is a Lewis acid and an effective catalyst for Friedel-Crafts alkylations (Figure 3.15). 

The procedure for preparing supported aluminium chloride relies on the small but significant solubility of aluminium chloride in aromatic hydrocarbons (typically toluene) and the slow reaction of the dissolved A1C13 with the surface hydroxyls of a commercial silica gel or acid-treated clay (Figure 1). One mole equivalent of HC1 is produced during the catalyst preparation consistent with the formation of mostly -OAlCl2 units on the surface and the use of hot solvent is essential so as to force the reaction and to ensure that the HC1 is driven from the system. 

In some cases the heterogeneous version of a catalyst can be prepared by direct reaction of that catalyst with a suitable support material. Thus reactive Lewis acids such as aluminium chloride will react with hydroxylated materials such as silica gel to give directly bonded surface species such as -OAICI2.20 Another single-step route to the supported catalyst is via sol-gel techniques, typically to produce an organically modified mesoporous silica. This is based on the co-polymerisation of a silica precursor and an organosilicate precursor (Figure 1.5). 

More recently, it has been shown that it is possible to extend the methodology for supported aluminium chloride for liquid-phase applications to hexagonal mesporous silicas as supports (HMSs and including MCM materials).115,116 Activity in the alkene alkylation of alkylaromatics is again comparable to that of A1C13 itself, and the solid adds are also easily recovered and can be reused. Most significantly, the increase in selectivity towards monoalkylation through... 

Boroujeni, K. P. and Parvanak, K. 2011. Efficient and solvent-free synthesis of bis-indolyl-methanes using silica gel-supported aluminium chloride as a reusable catalyst. Chin. Chem. Lett. 22(8) 939-942. 

The high-density polyethylene is linear and can be manufactured by (i) coordination polymerisation of monomer by triethyl aluminium and tritanium chloride, (ii) polymerisation with supported Metal Oxide Catalysts. Such as chromium or molybdenum oxides supported over alumina-silica bases. 

The EDX spectrum (Fig. 11.8) shows the main surface scale impurity peaks of silica, aluminium, sodium, chloride and iron. If this EDX is compared to that of a new, clean membrane surface (Fig. 11.9), the clean surface shows sulphur, carbon and oxygen, which is typical of a porous polysulphone support. It was concluded that the scale is amorphous, composed of aluminosilicate and silicate. These compounds are normally found in trace amounts in brine solutions. Analysis showed that the surface could be cleaned with hydrochloric acid and analysis of the dissolved scale was similar to the EDX spectrum analysis. Review of the plant operation determined that the precipitation was the result of high pH in combination with high silica concentrations in the brine. 

In drop-coagulation to form beads of alumina hydroxide, the top of a column holding oil and 100°C is fed with a blend of a sol of aluminium oxychloride and hcxamcthylcnc tctraminc. Under the influence of the temperature, the amine is decomposed to liberate ammonia, which neutralizes the chloride ions. The product is then ripened, dried, calcined and can be used as a support for reforming catalysts or hydrodesulfurization catalysts [2], In the same way. a silica sol feeding the bottom of a column of trichloroethylene at around 75 °C permits obtaining silica beads at the top. 

An important fact to remember is that an interaction of a metal precursor with an oxide support modifies the support and very often a part of the support dissolves [33]. So, for example, aluminium from AI2O3 appears in the liquid phase as chloride, oxychloride, hydroxynitrate, etc. The same holds for oxides of V, Ta, Nb, Ti, Zr and others. On the other hand, silica can be partially dissolved when NH3-containing precursors are used. When water or another solvent is removed upon drying, the species formed from the support can appear on the surface of the precursor crystallites and finally, after reduction, on the metal. (Note, a high temperature reduction would remove a volatile AICI3, a low temperature reduction would not.) For certain reactions this could be a way of creating promoters from the support. 

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