Synthesis and Characterization of n-Alkylamine-Stabilized Palladium Nanoparticles for Electrochemical Oxidation of Methane

Palladium nanoparticles (PdNPs) have been synthesized using n-alkylamines (C-n-NH2) as stabilizing ligands. The NP size and distribution were controlled 1)), varying the initial mole ratio of PdCl2/C-n-NH2 and carbon chain lengths of C-n-NH2 including hexylamine (C-6-NH2), dodecylamine (C-12-NH2), and octadecylamine (C-18-NH2). The average PdNP sizes were 20 +/- 2.0, 6.0 +/- 0.8, 5.6 +/- 0.8, 6.5 +/- 0.9, and 5.2 +/- 0.8 nm prepared with 1:7 PdCl2/C-6-NH2, 1:7 PdCl2/C-12-NH2, 1:7 PdCl2/C-18-NH2, 1:5 PdCl2/C-18-NH2, and 1:9 PdCl2/C-18-NH2, respectively. The particle size decreased with the increase in the carbon chain length of C-n-NH2. The as-synthesized n-alkylamine stabilized PdNPs (C-n-NH2-PdNPs) were fully characterized by transmission electron microscopy, X-ray powder diffraction, UV-visible absorption spectroscopy, infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), proton nuclear magnetic resonance (H-1 NMR) spectroscopy, thermogravimetric analysis, graphite furnace atomic absorption spectrometry, and mass spectrometry. The interaction of C-18-NH2 with PdNPs was verified by IR, XPS, and H-1 NMR spectra, demonstrating that the amine functionalities were Successfully linked to the Pd core Surfaces. The PdNPs are soluble and stable in apolar solvents Such as benzene, chloroform, n-hexane, and toluene. The electrochemical reactions between CH4 and C-n-NH2-PdNPs oil Pd electrodes were studied by cyclic voltammetry and chronoamperometry. These PdNPs reacted readily and produced good response to CH4 at ambient conditions. The sensitivity to CH4 depends on file PdNPs prepared from various n-alkyl chain lengths of C-n-NH2 and also the mole ratio of PdCl2/Cn-NH2. It wits determined that PdNPs synthesized from 1:7 PdCl2/C-18-NH2 displayed the best electrocatalytic oxidization Of CH4. The C-18-NH2-PdNP (5.6 nm) modified Pd electrode Could be used repeatedly and had a stable and reproducible response to CH4.