The partial oxidation of methane over Pd/Al2O3 catalyst nanoparticles studied in-situ by near ambient-pressure x-ray photoelectron spectroscopy

Near ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) is used to study the chemical state of methane oxidation catalysts in-situ. Al2O3{supported Pd catalysts are prepared with different particle sizes ranging from 4 nm 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 in- creases, from metallic Pd0 to PdO, and back to Pd0. 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 H2. A particle size effect is observed, such that CH4 conversion starts at lower temperatures with larger sized particles from 6 nm to 10 nm. We find that all nanoparticles begin CH4 conversion at lower temperatures than polycrystalline Pd foil

Oxygen-Induced Thermal Faceting of Pd Nanosized Crystals

The oxygen-induced faceting of [111] and [100] oriented Pd nanosized crystals (“tips”) was studied by field ion microscopy (FIM). Annealing at temperatures of 500 K in the presence of submonolayer amounts of oxygen caused major reconstruction to occur. Regions of the {100} plane broke up into small {100}, {112}, and {012} facets. In addition, only {111} and significantly enlarged {011} facets occurred at the surface of the reconstructed Pd crystal. The faceting behavior is in accordance with recently calculated equilibrium shapes of Pd crystals in the presence of small amounts of adsorbed oxygen.info:eu-repo/semantics/publishe