Ni-Pt loaded silicoaluminophosphate molecular sieves for hydroisomerisation of n-heptane

Silicoaluminophosphates SAPO-5 and SAPO-11 were hydrothermally synthesised and loaded with 0.2 wt.% Pt and varying (0, 0.2, 0.4 and 0.6 wt.%) amount of Ni. The line broadening XRD and TEM analyses of Ni-Pt/SAPOs indicate that the average size of Ni-Pt particles increases with increasing Ni addition. The ESCA studies reveals that complete reduction of Ni is observed only up to 0.4 wt.% Ni addition. The acidity of the catalysts analysed by TPD of ammonia revealed that added Ni species occupy the acid sites of SAPOs. Catalysts 0.4 wt.% Ni and 0.2 wt.% Pt loaded SAPOs show enhanced activity in n-heptane conversion, isomerisation selectivity and stability of the catalysts. Further, the selectivity towards the multibranched (MTB) isomers by protonated cyclopropane (PCP) intermediate formation is enhanced over the above catalysts. SAPO-5 based Ni-Pt catalysts show better activity than SAPO-11 based catalytic systems. (C) 2004 Elsevier B.V. All rights reserved.