A study of the influence of the synthesis conditions upon the catalytic properties of silicoaluminophosphate molecular sieves

The skeletal isomerization of 1-butene was performed over a series of silic oaluminophosphate molecular sieves with AEL structure (SAPO-11). The result s were compared with those obtained over an aluminophosphate molecular siev e (AlPO4-11). The three SAPO-11 samples, with different acidic properties, were synthesized by either varying the chemical composition of the synthesi s gel or by varying the preparation time of the aforementioned gel. The cat alytic results indicate that irrespective of how the acidity of the SAPO-11 samples is changed (viz., independently of the method elected to modify th e acidic properties of the samples), a close parallelism between the select ivity towards the skeletal isomerization and the number of (moderate + stro ng) Bronsted acid sites (sites retaining pyridine above 623 K) was observed for the SAPO-11 solids. These results, definitively, indicate the particip ation of these acid sites in the skeletal isomerization process.