The hydroconversion of n-decane has been investigated over bifunctional Pt/MCM-41//MgAPO-n (n = 5, 11) composite catalysts consisting of Pt/MCM-41 as the metal function and different Mg-containing aluminophosphates MgAPO-n as the acidic function. Hydrocracking is dominant over the catalysts containing MgAPO-5, while the isomerization selectivity is high over composite catalysts containing MgAPO-11. The higher isomerization selectivity of the latter catalysts is explained in terms of shape selectivity. The acid site density was varied by adding different quantities of MgAPO-n to the composite catalyst without changing the overall metal content. The highest selectivity for n-decane isomerization is found for a 50/50 physical mixture of 1.0Pt/MCM-41 with MgAPO-11. The distance between the two catalytic functions was varied by mixing of different sized pellets. It was found that the particles with diameters ranging from 1 to ca. 250 mum can be mixed without significant decrease in catalytic activity. The results of this study confirm that the classical bifunctional mechanism for isomerization and hydrocracking of n-alkanes is operative under our experimental conditions. (C) 2003 Elsevier Science (USA). All rights reserved.