Investigation of Parameters Influencing the Activation of a Pd/γ-Alumina Catalyst during Methane Combustion

Abstract

The progressive activation of a Pd(2 wt %)/gamma-alumina catalyst under the reaction conditions of catalytic combustion of methane (CCM) was studied. The reasons of this activation were investigated by XPS, CO-chemisorption, and HR-TEM. The removal of carbon from the surface cannot explain the observed activation process. Sintering of the palladium particles was detected but this parameter alone does not fully explain the activation process of the catalyst. HR-TEM imaging evidences (i) that PdO is present both in the fresh and the active catalyst and (ii) that the PdO nanoparticles sinter and restructure (surface roughening) during the reaction. Development of preferential faces was not observed. It is suggested that this restructuring may be responsible for the activation process by facilitating the formation of an active oxygen layer on the PdO surface. CCM on Pd/gamma-Al(2)O(3) depends on the thermal history of the catalyst and is a structure-sensitive reaction.

Investigation of the behaviour of a Pd/γ-Al2O3 catalyst during methane combustion reaction using in situ DRIFT spectroscopy

“…Moreover, this oxidized surface state after test was observed even after an in situ reducing pre-treatment [30], or after a test in presence of low amounts of H 2 in the CCM feed [31,32].…”

“…In addition, this investigation was also motivated by the experimental observation that, in our conditions, the surface of a powdered Pd (2 wt.%)/g-Al 2 O 3 catalyst was always in www.elsevier.com/locate/apcata Applied Catalysis A: General 295 (2005) [59][60][61][62][63][64][65][66][67][68][69][70] oxidized form after a conventional micro-reactor test [29][30][31][32]. Moreover, this oxidized surface state after test was observed even after an in situ reducing pre-treatment [30], or after a test in presence of low amounts of H 2 in the CCM feed [31,32].…”

In situ study of the formation and stability of supported Pd2Ga methanol steam reforming catalysts

“…We observed the disappearance of the Ga 0 signal indicating decomposition of the intermetallic compound and reoxidation of the incorporated zero-valent Ga in the XPS-probed surface region. Additionally, the Pd 3d signal decreased in intensity by 60% and, although Pd(111) and supported nanoparticles have been shown to form PdO (E b > 336 eV) at comparable conditions [44,46,47], Pd remains in a metallic state. These observations point to the formation of a Ga x O y overlayer or islands on the particle surface during oxidative decomposition of the intermetallic.…”

Steady State Isotopic Transient Kinetic Analysis of Flameless Methane Combustion over Pd/Al2O3 and Pt/Al2O3 Catalysts

“…The methane molecule may adsorb both on the palladium and palladium oxide, and the activity of the palladium catalyst is very closely related to the presence of oxidised palladium. Palladium oxide is presented at the temperatures, at which the process of the methane oxidation begins, even over the pre-reduced palladium catalyst [26,27]. The amount of palladium oxide increases simultaneously with the increase of the reaction temperature.…”