In Situ Generation of Pd/PdO Nanoparticle Methane Combustion Catalyst: Correlation of Particle Surface Chemistry with Ignition

Abstract

Decomposition of a fuel-soluble precursor was used for in situ generation of Pd/PdO nanoparticles, which then catalyzed ignition of the methane/O2/N2 flow. To help understand the relationship between particle properties and activity, the composition, structure, and surface chemical state of the particles were determined by a combination of high-resolution transmission electron microscopy (HRTEM), electron diffraction, scanning transmission electron microscopy/energy dispersive X-ray spectroscopy (STEM/EDX), and X-ray photoelectron spectroscopy (XPS). The particles, collected under methane-free conditions, were found to be primarily crystalline, metallic Pd, with TEM results showing a narrow size distribution around 8 nm and scanning mobility particle sizing measurements (SMPS) indicating a median particle size of ∼10 nm. The ignition temperature was lowered ∼150 K by the catalyst, and we present evidence that ignition is correlated with formation of a subnanometer oxidized Pd surface layer.

Flame-Made WO3/CeOx-TiO2 Catalysts for Selective Catalytic Reduction of NOx by NH3

“…The interplanar distance (d) was measured by averaging the distances between successive peaks in the contrast profile taken along a line perpendicular to the fringes in the software DigitalMicrograph. 33 X-ray diffraction (XRD) analysis was performed using a Bruker D8 Advance diffractometer equipped with a Ni-filtered Cu-Kβ radiation and a LinxEye detector. The diffraction patterns were collected in the range of 5 o <2θ< 80 o .…”

In situ X-ray Scattering and Dynamical Modeling of Pd Catalyst Nanoparticles Formed in Flames

“…Devener et al 4 demonstrated that an organopalladium compound injected into a gas-phase flow reactor with fuel was effective at catalyzing methane ignition and that ignition required formation of metallic Pd nanoparticles with a monolayer of oxide on the surface.…”

“…One uses organic ligands functionalized on catalyst nanoparticles to achieve solubility, 5−9 and the other employs a fuel-soluble organometallic precursor that can transform itself rapidly to catalyst nanoparticles in a reacting flow. [2][3][4]10 In particular, both nanoparticles and organometallic compounds containing Pd have been proposed for this application. [2][3][4]6,9,10 For example, Shimizu et al 3 …”

Temperature-dependent gas-surface chemical kinetic model for methane ignition catalyzed by in situ generated palladium nanoparticles

“…Palladium (Pd) nanoparticles have been proposed as a catalyst for low-temperature ignition of hydrocarbon fuels for hypersonic propulsion [1,2]. When generated in situ in a flow reactor by oxidation of an organometallic precursor, Pd can lower the ignition temperature of methane-air mixtures significantly [1].…”

“…Subsequent condensation leads to Pd particles formation in a mixture containing methane, oxygen, and nitrogen. These nanoparticles are 10-20 nm in diameter and consist of a crystal palladium core and a few atomic layers of palladium oxides [2]. Kinetic modeling using a combined gas-phase and gas-surface reaction model suggested that ignition occurs due to a two-stage reaction process.…”