Catalysis acidic borosilicate

Elements such as B, Ga, P and Ge can substitute for Si and A1 in zeolitic frameworks. In naturally-occurring borosilicates B is usually present in trigonal coordination, but four-coordinated (tetrahedral) B is found in some minerals and in synthetic boro- and boroaluminosilicates. Boron can be incorporated into zeolitic frameworks during synthesis, provided that the concentration of aluminium species, favoured by the solid, is very low. (B,Si)-zeolites cannot be prepared from synthesis mixtures which are rich in aluminium. Protonic forms of borosilicate zeolites are less acidic than their aluminosilicate counterparts (1-4). but are active in catalyzing a variety of organic reactions, such as cracking, isomerization of xylene, dealkylation of arylbenzenes, alkylation and disproportionation of toluene and the conversion of methanol to hydrocarbons (5-11). It is now clear that the catalytic activity of borosilicates is actually due to traces of aluminium in the framework (6). However, controlled substitution of boron allows fine tuning of channel apertures and is useful for shape-selective sorption and catalysis. 

Although adsorption processes represent an extremely large application of molecular sieves (49), applications in the area of heterogeneous catalysis have received the most attention for borosilicate molecular sieves. Due to the inherently weaker acidity of borosilicates relative to aluminosilicates, a number of advantages in using borosilicates have been reported due to improved product distributions or reaction selectivities. 

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. 

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