Wetting phenomena during alternating heating in O2 and H2 of supported metal crystallites

Influence of the addition of H2 upon the behavior and properties of a Pd(2wt.%)/γ-Al2O3 catalyst and a comparison with the case of the Pt-based catalyst

“…The origin of the more extended sintering of the palladium particles when some H 2 is present in the CCM feed could be the more reductive atmosphere obtained when adding H 2 . Indeed, reductive media favor the appearance of metallic palladium and their rapid coalescence into larger particles, whereas oxidant atmospheres cause reoxidation of metallic palladium into PdO particles which spread onto the alumina support [51,52]. This explanation is well supported by the XPS and Pd dispersion measurements.…”

“…Indeed, it is well known that the temperature is a key parameter controlling the dispersion of palladium [53]. More precisely, sintering of palladium particles is favored at high temperature [51,52].…”

Coverage of palladium by silicon oxide during reduction in H2 and complete oxidation of methane

“…In our work (Table 1), the higher surface area for the oxidized catalysts was caused probably by palladium surface roughening during O 2 oxidation, although the TEM pictures presented here do not suggest a substantial difference in surface roughening between reduced and oxidized samples. Ruckenstein and Chen [51] suggested that a particle breakup, not observed by TEM in our experiments either, could be the explanation for higher surface area. Datye [24] suggested based on TEM results that the surface of Rh catalysts was roughened when the sample was oxidized in O 2 and then reduced in H 2 at a mild temperature.…”

Investigation of the physico-chemical implications of the hydrogen presence during H2-assisted catalytic combustion of methane using Pd(10wt.%)/γ-Al2O3 catalyst

“…The effect of hydrogen on the dispersion of palladium is thus to sinter the particles, independently of its concentration. The presence of hydrogen is indeed reported to favour the sintering of metallic particles [33,34]. This could be explained by the fact that hydrogen can modify the oxidation state of palladium, can produce water by combustion, and can locally increase the temperature of the reactant medium due to its highly exothermal combustion reaction.…”