Activity of Carbon-Supported Platinum Nanoparticles toward Methanol Oxidation Reaction:  Role of Metal Precursor and a New Surfactant, tert-Octanethiol

Two groups of carbon-supported platinum nanoparticle catalysts have been prepared. In group I, catalysts I and II were prepared using PtCl 4 and H 2 PtCl 6 as starting materials and 1-hexanethiol, HSCH 2 CH 2 CH 2 CH 2 CH 2 CH 3, as a surfactant. For group II, the same platinum complexes were used as starting materials (catalyst III from PtCl 4, catalyst IV from H 2 PtCl 6 ) and tert -octanethiol, HSC(CH 3 ) 2 CH 2 CH 2 CH 2 CH 2 CH 3, was used as a surfactant for the first time. It has been found that the group II catalysts are between ∼2 and ∼3.3 times more active toward methanol oxidation reaction compared to other prepared and commercial catalysts. Transmission electron microscopy shows that the platinum nanoparticles are homogeneously dispersed on the carbon support and exhibit a narrow size distribution; the average particle size was found to be 2 ± 0.4 and 3 ± 0.4 nm in diameter for group I and group II catalysts, respectively. X-ray diffractogram analysis indicates that the platinum nanoparticles have a face centered cubic structure consistent with that of platinum metal itself. X-ray photoelectron spectra of the catalysts indicate two different types of platinum with the Pt 4f 7/2 binding energies of 71.1, 74.4 eV; 71.3, 74.3 eV; 71.0, 74.4 eV; and 71.5, 74.5 eV for catalysts I−IV, respectively. These have been identified as Pt(0) and Pt(IV), which could be platinum oxide or hydroxide. By looking at the oxidation state data, we found that catalysts I−IV consist of 71% Pt(0) and 29% Pt(IV); 83% Pt(0) and 17% Pt(IV); 76% Pt(0) and 24% Pt(IV); and 65% Pt(0) and 35% Pt(IV), respectively.