The effect of Pt content on the light naphtha isomerization reaction was studied using PtGaZr/SiO2-type catalysts. The catalysts were characterized by XPS, IR, pyridine, and CO adsorption, and by chemical reaction. The reaction was studied in a radial plug flow-type gas-phase reactor at three temperature levels, residence times, and hydrogen partial pressures. Other exploratory tests involved adding 20% of 1-pentene, cyclopentane, or isopentane to the feedstock. The results indicate that Pt is incorporated into the Ga-Zr and Ga-Si cluster, which is generated by migration of Ga and Zr to the surface of the silica. The Pt slightly modifies the number, activity, and selectivity of the acid sites, but its most important role is on catalyst stability. It was found that some Pt delta+ species may be located in the border of the crystal, and Pt2+ species may be found in the subsurface of the clusters. A mechanism of two isomerization acid sites proposed, and an apparent kinetics model for light naphtha isomerization is used to predict the isomer yields in a gas-phase radial reactor. The role of catalysts surface composition in chemical reactions is discussed. (c) 2008 Elsevier Inc. All rights reserved.