Preparation of Stable Exfoliated Pt−Clay Nanocatalyst

Abstract

In this paper, we report a novel experimental protocol for the preparation of stable and exfoliated nano-Pt catalysts supported on layered silicate clay surfaces. Uniformly dispersed highly crystalline Pt nanoparticles with diameters between 2 and 5 nm were chemically adsorbed on to the layered silicate surfaces using a chemical vapor deposition (CVD) method employing organoclay as the initial support. The as-prepared catalysts were found to be extremely stable against both intensive mechanical agitation and high temperature treatment. No Pt loading or morphology changes were observed after ultrasonication under a sonication power density of 6 MW/m(3) for up to 72 h at room temperature or annealing at 700 degrees C for 1 h under Ar flow. On the other hand, Pt catalysts prepared using the inorganic clay as the initial support were found to be highly unstable against both mechanical agitation and high temperature treatment. Significant leaching and catalyst restructuring or sintering was observed. Exfoliation of catalysts and the nature of Pt adsorption were elucidated by systematic analysis using wide-angle X-ray diffraction (WAXD) analysis, Brunauer-Emmett-Teller (BET) surface area analysis, and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) analysis. No low angle diffraction peak was observed in the WAXD pattern, and a 700% increase in BET surface area was observed after Pt deposition on clay surfaces. Depth profiling ToF-SIMS on Pt deposited on SiO(2) wafer surfaces showed the presence of PtSiO ion at the Pt and SiO(2) interface. This ion group was also detected in the bulk of Pt-OrC catalyst, confirming chemisorption of Pt on layered silicate clays. A much lower concentration of PtSiO ion was observed in the Pt-NaC with a similar Pt loading. In addition, X-ray photoelectron spectroscopy (XPS) shows that the binding energy of Pt4f(7/2) in Pt-OrC is much higher than that in the Pt-NaC. The protocol reported in this paper can also be applicable to other clay supported stable metallic catalysts.