Volumetric distribution of Pt nanoparticles supported on mesoporous carbon substrates studied by X-ray photoelectron spectroscopy depth profiling

We present an X-ray photoelectron spectroscopy depth profiling study of the size and volumetric distributions of Pt nanoparticles supported on two mesoporous carbons. Based on the analysis of the chemical shift of the Pt4f peaks, we found the one with a mesopore diameter of ∼5 nm has a uniform distribution of crystalline Pt nanoparticles throughout the porous body. In contrast, the other with a mesopore diameter of ∼3 nm has a distinct distribution of crystalline Pt nanoparticles on the outermost surfaces of the porous material and extremely small (<1 nm) Pt nanoparticles in the interior region. The small Pt particle size in the interior represents the effect of pore entrance blockage of those mesopore channels with diameter less than 3 nm. Such blockage gives rise to the encapsulation of very small amounts of Pt precursors inside the nanospace of the porous matrix, with the result that the particles grown in the interior region of the support are less than 1 nm in size.