Pd nanoparticle size is one of important factors to determine the catalytic activity of formic acid dehydrogenation catalysts. Thus various approaches to minimization of Pd nanoparticles have been attempted. In this study, we first tried to decrease Pd nanoparticles size and increase Pd dispersion of Pd/NH2-mesoporous silica (Pd/NH2-KIE-6) catalysts by controlling only stirring time and types of Pd precursors. It was demonstrated that the stirring time and types of Pd precursors significantly affect the performance of the catalysts. As a result, the Pd/NH2-KIE-6 exhibited the highest catalytic activity (TOF: 8185 mol H-2 mol catalyst-(1) H-1 ever reported for additive-free formic acid dehydrogenation at room temperature. In addition, the Pd/NH2-KIE-6 provided higher TOF even than the case with additives such as sodium formate. Considering that the catalytic activity of Pd-based catalysts for formic acid dehydrogenation was previously controlled by promoter, support type and surface chemistry of supports, controlling the stirring time and types of Pd precursors is novel and very intriguing solutions to go beyond the current kinetic limitation for formic acid dehydrogenation. (C) 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.