The Partial Oxidation of Methane Over Pd/Al2O3 Catalyst Nanoparticles Studied In-Situ by Near Ambient-Pressure X-ray Photoelectron Spectroscopy

Abstract

Near ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) is used to study the chemical state of methane oxidation catalysts in-situ. Al 2 O 3-supported Pd catalysts are prepared with different particle sizes ranging from 4 to 10 nm. These catalysts were exposed to conditions similar to those used in the partial oxidation of methane (POM) to syn-gas and simultaneously monitored by NAP-XPS and mass spectrometry. NAP-XPS data show changes in the oxidation state of the palladium as the temperature increases, from metallic Pd 0 to PdO, and back to Pd 0. Mass spectrometry shows an increase in CO production whilst the Pd is in the oxide phase, and the metal is reduced back under presence of newly formed H 2. A particle size effect is observed, such that CH 4 conversion starts at lower temperatures with larger sized particles from 6 to 10 nm. We find that all nanoparticles begin CH 4 conversion at lower temperatures than polycrystalline Pd foil.

Operando characterisation of alumina-supported bimetallic Pd–Pt catalysts during methane oxidation in dry and wet conditions

“…Under stoichiometric wet conditions, the 2.5Pd-2.5Pt had a higher TOF than 5.0Pd, but a lower TOF under oxygen excess wet conditions. For monometallic palladium catalysts, the TOF values follow the same order as the average particle sizes: 5.0Pd < 2.5Pd < 4.0Pd, in line with earlier findings by Price et al for partial methane oxidation [35]. This trend was partially maintained under wet conditions, but with all catalysts having a lower turnover frequency, and 2.5Pd now showing a lower TOF than 5.0Pd.…”

Enhanced Photocatalytic Performance toward CO2 Hydrogenation over Nanosized TiO2-Loaded Pd under UV Irradiation

“…This phenomenon indicates the generation of a new surface species, namely, Pd C, and the increased magnitude of the C 1s peak at 284.6 eV in the survey spectrum in Figure 8a also supports this conclusion. 48,49 The formation of PdC surface species is helpful to explain the reaction mechanism of the photocatalytic hydrogenation of CO 2 .…”

Ambient Pressure Photoelectron Spectroscopy: Opportunities in Catalysis from Solids to Liquids and Introducing Time Resolution

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