Fine Dispersion of Pt_4–5 Subnanoclusters and Pt Single Atoms over Porous Carbon Supports and Their Structural Analyses with X-ray Absorption Spectroscopy

Abstract

We demonstrate the fine dispersion of Pt4–5 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 (∼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.

Constraint spaces in carbon materials

“…Loading of subnanometer-sized Pt clusters (Pt 4-5 ) onto carbon materials was shown to be possible by conning a Pt precursor into their micropores. 60 An organometallic precursor, (COD) PtMe 2 (COD: 1,5-cyclooctadiene) was selected as a Pt precursor, which was strongly adsorbed in the micropores of carbon substrates by a wet impregnation technique and easily reduced by a thermal treatment. Ketjenblack (KB; S BET : 1290 m 2 g À1 , V micro : 0.46 cm 3 g À1 ) and zeolite-templated microporous carbon (ZTC; S BET : 3680 m 2 g À1 , V micro : 1.55 cm 3 g À1 ) were employed as carbon substrates.…”

The loading effect of Pt clusters on Pt/graphene nano sheets catalysts

“…Graphene as well as a supporting material may assist to homogenize and disperse noble metals 26 , 27 , to generate metal clusters 28 , reducing CO oxidation reaction by assisting strong interactions between support–cluster 29 , and protecting Pt cores on fuel cells operating system 30 . Pt nanoparticles have been applied as catalysts on fuel cells 31 .…”

Highly dispersed Pt nanoclusters supported on zeolite-templated carbon for the oxygen reduction reaction

“…32 Among the microporous carbons, zeolitetemplated carbon (ZTC) has been attractive for supporting Pt clusters due to its ordered microporous structure. [33][34][35][36][37] ZTC is a potentially promising material as catalyst support as it offers the advantages of extremely large surface area and high electrical conductivity of graphene-like carbon frameworks constituting a three-dimensional (3D) interconnected pore structure. 36 Moreover, the micropores of ZTC can serve as nanocages for stabilization of the Pt nanoclusters.…”

“…23 Itoi et al synthesized PtNC consisting of 4-5 atoms and a single Pt atom in ZTC using the organoplatinum complex. 37 Although these methods produced Pt nanoclusters with narrow size distribution and atomic dispersion, they required multi-step processes and/or high-temperature treatment (>300 C). Hightemperature treatment oen induces the sintering of nanoclusters to aggregated clusters.…”