Hydrogen chloride is commonly present in syngas produced from municipal solid waste and biomass gasification. The influence of HCl on the activity of nickel-based catalysts during catalytic naphthalene reforming was investigated. Two synthesized and two commercial catalysts were tested for steam reforming at 790 degrees C and SV 24,000 h(-1). In the absence of HCl, nickel supported on limestone (Ni/Limestone) demonstrated lower naphthalene conversion (similar to 80%) compared to nickel supported on alumina (Ni/Alumina) and two commercial alumina supported catalysts (similar to 100%). In the presence of 2000 ppmv HCl, the naphthalene conversion of Ni/Limestone rapidly decreased due to the reaction with HCl and, probably, formation of molten CaCl2 deactivating the supported Ni nanoparticles. These data demonstrate limited applicability of calcium-based nickel catalysts for naphthalene reforming at the studied temperature. The efficiencies of Ni/Alumina and two commercial catalysts were maintained at similar to 100% naphthalene conversion. However, HCl concentrations of 500-2000 ppmv had detrimental effect on water-gas shift activity of alumina supported catalysts during naphthalene reforming. The spent alumina supported catalysts were characterized by N-2 adsorption, FESEM/EDS, XRD, XPS, TPR and TEM after the reforming in the absence and presence of HCl, and the results suggested that HCl increased nickel sintering in the catalysts causing the loss of water-gas shift activity. The losses of catalytic activity varied among the catalysts and were the lowest for Ni/Alumina, which contained nanosized porous alumina support and had the strongest Ni nanoparticle-support interactions.