Influence of pH and Si content on Si incorporation in SAPO-5 and their catalytic activity for isomerisation of n-heptane over Pt loaded catalysts

SAPO-5 samples have been synthesised using N-methyldicyclohexylamine as structure-directing agent (SDA) over a wide range of both Si content and pH values of the starting gel. The samples have been characterised in detail by XRD, DRIFT, N2 adsorption, TPD of pyridine and multinuclear MAS NMR. Pt loaded SAPO-5 samples were tested for hydroisomerisation of n-heptane; samples prepared at high pH (ca. 9) showed good catalytic activity, which is in agreement with the nature extent of Si(IV) incorporation deduced from both solid-state NMR and TPD of pyridine; samples prepared at low pH, as well as with higher Si content in the gel, seem to favour the formation of silica islands and consequently possess lower catalytic activity compared to the ones produced with low Si content and at high pH.