ISOMERIZATION OF N-HEPTANE OVER PD-LOADED SILICO-ALUMINO-PHOSPHATE MOLECULAR-SIEVES

Isomerization of n-heptane was studied on a series of bifunctional SAP O-based catalysts with contents of 0.1 wt% Pd. From results on tempera ture programmed desorption of NH3 it is deduced that the different mol ecular sieve structures contain nearly identical amounts of silicon su bstituting for phosphorus in the framework (0.3 to 0.5 silicon atoms p er unit cell). Best activities and selectivities for branched heptane isomers are achieved with SAPO-11 and SAPO-31. SAPO-17 and SAPO-5 show substantially lower activities. With SAPO-5, there is a high cracking selectivity which is assumed to be caused by the reduced accessibilit y of parts of the bridged hydroxyl groups within the molecular sieve f ramework. Different locations of these acid sites are evidenced by inf rared OH vibration spectra recorded after adsorption of n-heptane. (C) 1995 Academic Press, Inc.