Fine Dispersion of Pt4-5 Subnanoclusters and Pt Single Atoms over Porous Carbon Supports and Their Structural Analyses with X-ray Absorption Spectroscopy

We demonstrate the fine dispersion of Pt-4_5 subnanoclusters or Pt single atoms on two types of porous carbon supports, Ketjen black (KB) and zeolite-templated carbon (ZTC). The loading amount of Pt4_5 subnanoclusters reached as much as ca. 4 and 13 wt % for KB and ZTC, respectively. For the fine dispersion of Pt subnanoclusters, simply filling an organoplatinum complex, (COD)PtMe2, as a Pt precursor into the micropores is found to be crucial to prevent agglomeration or sintering of Pt subnanoclusters. Moreover, it is possible to disperse Pt single atoms on ZTC, simply by decreasing the Pt loading amount down to ca. 0.9 wt %, owing to some stabilization effect by oxygen-containing functional groups. The detailed structural insights into the supported Pt subnanoclusters and Pt single atoms were analyzed by X-ray absorption spectroscopy (XAS). Extended X-ray absorption fine structure (EXAFS) analysis for Pt subnanoclusters reveals that the Pt Pt bond is contracting to a large extent (similar to 2.8%) relative to balk values, and upon hydrogen chemisorption, the bond elongates more than the reported values for the 1.0 nm sized Pt-nanoparticles.