Synthesis and Dispersion of Dendrimer-Encapsulated Pt Nanoparticles on gamma-Al2O3 for the Reduction of NOx by Methane

Abstract

Dendrimer encapsulated Pt nanoparticles were prepared by using hydroxyl terminated generation four (G4OH) PAMAM dendrimers (DEN) as the templating agents. The encapsulated Pt nanoparticles were dispersed on gamma-Al2O3 at room temperature by impregnation. Pt/Al2O3 (DEN) catalysts were then subjected to thermal treatments in oxidizing and reducing atmospheres at different temperatures. These catalysts were characterized by Transmission Electron microscopy (TEM) and In situ Fourier-Transform Infrared (FTIR) spectroscopy. The TEM analysis of the as synthesized catalysts revealed that the Pt nanoparticles were found to be 2-4 nm in size. It is observed that the Pt particle size in 0.5% Pt/Al2O3 (DEN) catalyst increased upon thermal decomposition of the dendrimer. The in situ FTIR results suggested that the presence of oxygen and the Pt nanoparticles in the Pt-dendrimer nanocomposite accelerate the dendrimer decomposition at low temperatures. All the catalysts were tested for the reduction of NOx with CH4 in the temperature range of 250-500 degrees C. NOx reduction efficiency of Pt/Al2O3 (DEN) catalysts were compared with the Pt/Al2O3 (CON; conventional) catalyst. The conversion of NOx was started from the low temperatures over Pt/Al2O3 (DEN) catalysts. The high selectivity of NOx to N-2 of 74% was obtained over 0.5% Pt/Al2O3 (DEN) catalyst at low temperatures around 350 degrees C.