Catalytic properties of the silicoaluminophosphates SAPO-5 and SAPO-11 in n-octane and isooctane hydroconversion

The hydroisomerization and hydrocracking of n-octane and isooctane over Pt/SAPO-5 and Pt/SAPO-11 catalysts have been investigated in a microcatalytic pulse reactor operating at 3 bar and different temperatures (250–400 °C) and hydrocarbon pulse (0.5–5 µl). In all cases, Pt/SAPO-5 catalysts exhibit higher catalytic activity than Pt/SAPO-11, according to their higher adsorption values of pyridine and 2,6-dimethylpyridine. The primary products obtained with n-octane were the monobranched isomers and with isooctane were cracking products (especially isobutane), indicating that hydrocarbon structures impose different reaction mechanisms. The selectivity patterns found in this class of molecular-sieve catalysts are well interpreated in terms of a series of reaction pathways incroporating both confinement effects and shape-selectivity factors as being of importance in determining the observed product distribution.