The ability to synthesize well-defined and monodisperse nanoparticles allows the effect of particle size upon selectivity to be examined. In this work, the influence of Pt particle size was studied for pyrrole hydrogenation. Ultrasmall (as small as ~ 1 nm) Pt nanoparticles were synthesized by using fourth generation PAMAM dendrimers as the template and capping agent. Pt nanoparticles between 2 and 10 nm were synthesized using polymer (PVP) capping. Both series of nanoparticles were loaded onto mesoporous silica (SBA-15) by sonication. The scission of C-N bonds was observed to occur more readily when the Pt particles were larger than 2 nm and consequently n-butylamine and butane were more likely to form over larger nanoparticles. This trend is believed to occur because amine groups bind more strongly to and poison smaller nanoparticles. Characterization data, by techniques such as TEM, DRIFTS, elemental analyses (ICP-MS), XPS, and chemisorption, are also discussed.