The Structure–Sensitivity of n -Heptane Dehydrocyclization on Pt/SiO 2 Model Catalysts

The structure sensitivity of n -heptane dehydrocyclization has been evaluated on Pt nanoparticles as a function of Pt particle size. Pt particles were vapor-deposited onto a SiO 2 surface in ultrahigh vacuum (UHV) and then run under near-atmospheric pressures (495 Torr) by transferring the samples in situ to a batch reactor connected to the UHV system. The results demonstrate that the reaction rate increases as the particle size is decreased from 4 to 1.5 nm, consistent with results on high surface area technical catalysts. However, as particle size is further decreased below 1.5 nm, the reaction rate decreases, thus providing evidence of an optimum particle size for the dehydrocyclization reaction under the experimental conditions. The reactions on the nanoparticles are also compared with results obtained on Pt(100) and Pt(110) single crystals, which were run in the same apparatus under identical conditions. The differences between supported and unsupported Pt demonstrate that nanoparticles deactivate at a slower rate than single crystals, which suggests participation from the underlying silica support.