Vapor-phase hydrogenation of benzene and toluene over a size-dependent (1.5-5.2 nm) series of Pt nanoparticles (NPs) encapsulated in polyvinylpyrrolidone (PVP) or polyamidoamine (PAMAM) dendrimer and supported in SBA-15 mesoporous silica was investigated at ambient pressure between 343 K and 398 K. Under these conditions, both reactions exhibit a moderate structure sensitivity evidenced by changes in their turnover rate (TOR), apparent activation energy (E-A), pre-exponential factor In(r(o)), and deactivation rate parameters with Pt particle size. For instance, the 2.4-3.1 nm Pt NPs showed the highest TOR for both reactions as compared to NPs of either smaller or larger sizes. Also, the E-A and In(r(o)) factor values were larger for smaller Pt particle sizes, and the rates of catalyst deactivation were more pronounced for catalysts with larger Pt particle sizes. However, the reaction orders on H-2 and hydrocarbon were independent of particle size. Published by Elsevier Inc.