The hydrodearomatization of pyrolysis gasoline (PyGas) over bifunctional catalysts, based on noble metals (Pt, Pd, Ir, Ni) supported on a HY zeolite, has been studied in a fixed-bed reactor. The surface structures of the catalysts were determined by CO chemisorption, photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and temperature-programmed desorption of H-2 (H-2-TPD). Catalyst acidity was assessed by ammonia desorption measured by differential scanning calorimetry (DSC-NH3) and Fourier transform infrared spectroscopy of adsorbed pyridine (FFIR-Py). The kinetic performance and product selectivity of the catalysts were discussed in terms of the data provided by surface characterization techniques. Kinetic interpretation was carried out by using individual step conversion, i.e. hydrogenation and ring-opening. The results under mild ring-opening (MRO) conditions indicate a strong dependence of the hydrogenation activity on the metal used. Operating under severe ring-opening (SRO) conditions, a linear dependency of conversion and n-alkane yield on total acidity of the catalyst was observed. (c) 2006 Elsevier B.V. All rights reserved.