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.