Borosilicate catalysts

Borosilicate catalysts provide high approach to thermodynamic equilibrium of the xylenes, and offer high selectivity in the conversion of ethylbenzene (8.12.22.50 ). In addition, they have been shown to be less prone to the effects of thermal and steam treatments than corresponding aluminosilicate zeolite catalysts (51). The catalytic activity of borosilicate catalysts was demonstrated to be a function of the structural boron content of the molecular sieve (22.36,50). In addition, the by-product distribution obtained from a borosilicate catalyst in a xylene isomerization/ethylbenzene conversion process was found to be distinctive (50), with high transethylation reactivity relative to transmethylation. 

Methanol Conversion. Methanol conversion reactions based on borosilicate catalysts have been studied extensively (10.15,24,28.33.52-54). During the conversion of methanol, the reaction proceeds through a number of steps, to yield dimethylether, then olefins, followed by paraffins and aromatics. The weaker acid sites of borosilicate molecular sieves relative to those of aluminosilicates require higher reaction temperatures to yield aromatics. The use of less forceful process conditions leads to the formation of olefins selectively, instead of a mixture of paraffins, olefins, and aromatics (10.28.53.54). 

Borosilicate Catalysts, BorosHicates, which are prepared by the substitution of B for the Al in ZSM-5, are described as practical catalysts for shape-selective acid catalysis. The preferred application is the processing of Cg aromatics using isomerization, disproportionation, and transalkylation reaction steps. The borosilicate catalyst may also contain a metal additive, such as nickel or noble metal. 

Holderich has demonstrated the advantage offered by zeolite catalyst to the chemical industry. Many previously unknown synthesis steps are possible with zeolite catalysts. Two examples of the several dozens of potential and already implemented processes reviewed by Hdiderich are the synthesis of acetylimidazole, and the formation of isoprene from 3-methylbutylaldehyde. In the latter reaction a basic zeolite catalyst has a significantly longer lifetime than an acidic one. A surprising number of acid catalysed reactions use the extremely weakly acidic borosilicate analogs of ZSM-5 and other aluminium zeolites. These borosilicate catalysts contain less than 10 ppm Al. 

WUes and Watts [48,53] have reported the use of a rather successful heterogenic catalytic system to carry out these reactions. They have tested a borosilicate glass microreactor (dimensions 3.0 x 3.0 x 0.6 cm) consisting of two etched layers with two inlets, mixing channels, a larger etched region and the outlet. A solid-supported catalyst was dry-packed in this structure (Fig. 4). 

Asymmetric cyanosilylation of ketones and aldehydes is important because the cyanohydrin product can be easily converted into optically active aminoalcohols by reduction. Moberg, Haswell and coworkers reported on a microflow version of the catalytic cyanosilylation of aldehydes using Pybox [5]/lanthanoid triflates as the catalyst for chiral induction. A T-shaped borosilicate microreactor with channel dimensions of 100 pm X 50 pm was used in this study [6]. Electroosmotic flow (EOF) was employed to pump an acetonitrile solution of phenyl-Pybox, LnCl3 and benzal-dehyde (reservoir A) and an acetonitrile solution of TMSCN (reservoir B). LuC13-catalyzed microflow reactions gave similar enantioselectivity to that observed in analogous batch reactions. However, lower enantioselectivity was observed for the YbCl3-catalyzed microflow reactions than that observed for the batch reaction (Scheme 4.5). It is possible that the oxophilic Yb binds to the silicon oxide surface of the channels. 

Reactor Dimensions. Borosilicate glass tube, 10-mm. i.d., with 6-mm. o.d. thermocouple well down the center. The catalyst was supported on a sintered-glass disk. The empty tube was tested for catalytic activity and found inactive towards thiophene at temperatures up to 550° C. 

A conventional pulse catalytic microreactor was used with 15-65 mg of the catalyst for the cumene runs and 65 mg for the 2,3-dimethylbutane runs. The catalyst was held between 2 small plugs of borosilicate glass wool in a 5-mm ID diameter borosilicate reactor. In some experiments, the catalyst was diluted with 96% silica porous glass powder. The helium gas was purified by passage through alumina kept at liquid nitrogen temperature. The reaction temperature was measured by a thermocouple located adjacent to the reactor. The catalyst was pretreated at the desired temperature for 16 hours in a stream of helium. The products were analyzed with a dioctyl phthalate gas chromatography column at llO C. 

This review concerns the synthesis, characterization, and catalytic activity of microporous ferrierite zeolites and octahedral molecular sieves (QMS) and octahedral layer (OL) complexes of mixed valent manganese oxides. The ferrierite zeolite materials along with borosilicate materials have been studied as catalysts for the isomerization of n-butenes to isobutylene, which is an important intermediate in the production of methyltertiarybutylether (MTBE). The CMS materials have tunnels on the order of 4.6 to 6.9 A. These materials have been used in the total oxidation of CO to C02, decomposition of H2O2. dehydrogenation of CeHi4, C0H14 oxidation, 1-C4H3 isomerization, and CH4 oxidation. The manuscript will be divided into two major areas that describes zeolites and OMS/OL materials. Each of these two sections will include a discussion of synthesis, characterization, and catalytic activity. 

Substitution of either A1 or Si with various heteroatoms changes acid strength from the extremely weak acidity of borosilicates to the superacid-like strength of certain aluminosilicates. The acid sites of Ga- and Fe-silicates are weaker than those of their Al-analogs [35]. Several shape selective commercial processes use hetwoatom substituted molecular sieve catalysts. Iron-substituted pentasils (Encilite) are used for xylene isomerization and for producing ethylbenzene fi om benzene and ethanol [36,37]. 

The catalysts were pelletised, crushed and sieved the fraction with a diameter between 0.7 and 1.0 mm was collected. Reactions were performed downflow at atmospheric pressure with 1.00 g of material, stored under ambient in a borosilicate glass tube (i.d. 7 mm) heated by a fluidised bed oven. The catalysts were pretreated with ammonia/nitro-gen at 400°C to accomplish the reduction of Cu to Cu [8,9]. The reaction feed gas (33.4 ml/min) contained 16.5 vol% water or ammonia and 0.84 vol% chlorobenzene the WHSV (20°C) was 0.078 h (gp Q /gj,3 ). In experiments with other chloroaromatics, equal substrate vapour pressures and nucleophile/substrate ratios were used. Quantitative analysis was performed by on-line GC, product identification by mass spectrometry. 

Heated in borosilicate glass under N2 with Na in scc.-CaHyOil as a catalyst. 

From these experiments of Bone, from those of Henry mentioned in Chapter VI, and from those of Landolt,5 it has been concluded that hydrogen has been found to bum before methane at low temperatures in contact with platinum catalysts, and even at relatively high temperatures in platinum tubes 5 and that methane burns before hydrogen when exploded or when kept in borosilicate bulbs at moderate temperatures. 

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