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

Abstract

Palladium nanoparticles (PdNPs) have been synthesized using n-alkylamines (C n -NH 2 ) as stabilizing ligands. The NP size and distribution were controlled by varying the initial mole ratio of PdCl 2 /C n -NH 2 and carbon chain lengths of C n -NH 2 including hexylamine (C 6 -NH 2 ), dodecylamine (C 12 -NH 2 ), and octadecylamine (C 18 -NH 2 ). 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 PdCl 2 /C 6 -NH 2 , 1:7 PdCl 2 /C 12 -NH 2 , 1:7 PdCl 2 /C 18 -NH 2 , 1:5 PdCl 2 /C 18 -NH 2 , and 1:9 PdCl 2 /C 18 -NH 2 , respectively. The particle size decreased with the increase in the carbon chain length of C n -NH 2 . The as-synthesized n-alkylamine stabilized PdNPs (C n -NH 2 -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 ( 1 H NMR) spectroscopy, thermogravimetric analysis, graphite furnace atomic absorption spectrometry, and mass spectrometry. The interaction of C 18 -NH 2 with PdNPs was verified by IR, XPS, and 1 H 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 CH 4 and C n -NH 2 -PdNPs on Pd electrodes were studied by cyclic voltammetry and chronoamperometry. These PdNPs reacted readily and produced good response to CH 4 at ambient conditions. The sensitivity to CH 4 depends on the PdNPs prepared from various n-alkyl chain lengths of C n -NH 2 and also the mole ratio of PdCl 2 /C n -NH 2 . It was determined that PdNPs synthesized from 1:7 PdCl 2 /C 18 -NH 2 displayed the best electrocatalytic oxidization of CH 4 . The C 18 -NH 2 -PdNP (5.6 nm) modified Pd electrode could be used repeatedly and had a stable and reproducible response to CH 4 .

Hydrogen (H2) sensing and catalysis with organic-stabilized Pd and Pd alloy nanoparticles.

“…[36][37][38][39][40][41][42] Mayer and co-workers have studied extensively the stabilizing polymer on the reduction of an aqueous suspension of Ag, Au, Pt, or Pd ions by KBH 4 . [43][44][45][46] They investigated cationic polyelectrolytes, polyacids, non-ionic polymers, and block copolymers.…”

“…In fact, we observed from the TEM data that the particle size decreased with an increase in carbon chain length of CnS; therefore, smaller Pd NPs have larger organic weight fractions, which is in agreement with the literature. 39,42 This is also because a longer chain length has more mass. Among the CnS Pd NPs used, C18S Pd NPs produced the smallest Pd NPs (2.6 nm) with a high organic weight percent (39.3%).…”

“…17 In particular, their high surface area-to-volume ratio and size- in the application of these materials is the control of the size, shape, composition, and stability of the nanoparticles, 28,[116][117][118][119][120] which can be accomplished through synthesis and functionalization of the nanoparticles with organic stabilizers such as polymers, [24][25][26][27] dendrimers, [28][29][30][31][32] surfactants, [33][34][35] or ligands. [36][37][38][39][40][41][42] In 1994, Brust and co-workers reported, for the first time, an easy and reproducible synthesis for the preparation of Au NPs stabilized with self-assembled monolayers of dodecanethiolate ligands. 52 These roughly spherical particles have a core of metallic atoms surrounded by an organic monolayer.…”

“…Other metal NPs (Ag, 62 Pt, 37,38,41 Pd, 51,60,67 Ni, 167 and alloys 51,68,[168][169][170] ) have also been synthesized by the Brust reaction and used for sensing and catalysis applications. 38,39,67,68,123,131 Here we describe the chemical synthesis of Pd and Pd-containing alloy (PdAg)…”

“…37,41 Pd NPs coated with nalkylamines have also been used for the electrochemical oxidation of methane. 39 Astruc and co-workers investigated C12S Pd NPs for catalysis of the Suzuki-Miyaura C-C coupling reaction under ambient conditions. 40 Fornasiero and co-workers reported an approach for the preparation of Pd NPs coated with thiols and their easy recycling/reuse in the Suzuki cross-coupling reaction.…”