Preparation of Platinum/Carbon Aerogel Nanocomposites Using a Supercritical Deposition Method

Abstract

Platinum/carbon aerogel (Pt/CA) nanocomposites were synthesized using a supercritical deposition method. Dimethyl(1,5-cyclooctadiene)platinum (II) (CODPtMe2) was dissolved in supercritical CO2 (scCO2) and impregnated into porous organic and carbon aerogels. The impregnated aerogels were converted to Pt/CA composites by heat treatment ranging from 300 to 1000 °C in the presence of nitrogen gas. Both conventional and high-resolution TEM micrographs showed a good distribution of fairly monodisperse Pt particles throughout the bulk of all the aerogel supports used. The nature and crystallinity of the particles were confirmed using XRD. Increasing the reduction temperature increased both the crystal size and the polydispersity. Crystallite sizes as small as 1 nm were obtained at low reduction temperatures and the particles were single-crystalline. Particle sizes obtained from H2 and CO chemisorption measurements are consistent with those measured from TEM images, indicating the accessibility of the surface of platinum crystallites. The adsorption isotherm for the scCO2−CODPtMe2−CA system was measured at 28 MPa and 80 °C and indicated a strong substrate-precursor interaction which was also corroborated by thermogravimetric analyses (TGA). The isotherms also showed that Pt loadings as high as 40 wt % could be achieved. The results of this study demonstrated that in SCF deposition, it is possible to control the dispersion of metal crystallites on various supports through the strength of the interactions between metal precursors and the substrate and the reduction temperature.

Synthesis methods of low-Pt-loading electrocatalysts for proton exchange membrane fuel cell systems

“…This promising catalyst preparation technique results in small particle sizes and homogeneous dispersions [94e97]. An additional advantage of this technique is the ability to thermodynamically control [98,99] the metal loading. Bayrakçeken et al [100] used supercritical deposition technique to prepare Pt-based electrocatalysts for polymer electrolyte membrane fuel cells.…”

Activity, selectivity, and methanol tolerance of novel carbon-supported Pt and Pt3Me (Me = Ni, Co) cathode catalysts

“…For comparison, we included two commercial Pt/ C catalysts with different Pt loading (E-Tek Inc., 20 and 40 wt.% Pt), which also allowed conclusions on possible noble metal loading effects. The catalysts were synthesized via the so-called organometallic route, depositing preformed colloidal Pt, and Pt 3 Me pre-cursors on a high-surface area carbon support (see below) [27][28][29][30]. In contrast to the commonly applied method for preparing carbon-supported PtMe alloy catalysts, involving deposition of the non-precious metal on a carbon-supported Pt catalyst prepared beforehand, followed by alloying at high temperatures (T > 700°C), we expect this method to avoid substantial metal particle growth by sintering and coalescence during the high-temperature treatment.…”

Hydrodesulfurization of model diesel using Pt/Al2O3 catalysts prepared by supercritical deposition

“…The deposited precursor was reduced thermally at 300 8C in the presence of nitrogen gas with a flow rate of 100 cm 3 /min. The choice of the reduction temperature was based on TGA of the precursor [20]. The thermal decomposition was continued for 6 h. The commercial 0.52 wt.% Pt/Al 2 O 3 was purchased from Aldrich.…”

“…Recently, we reported on the synthesis of carbon aerogel supported platinum using a supercritical deposition method with good control of average platinum particle size [20]. In this method, dimethyl(1,5-cyclooctadiene)platinum(II) (CODPtMe 2 ) was dissolved in supercritical CO 2 (scCO 2 ) and impregnated into porous organic and carbon aerogels.…”