Oberflächengebundene Intermediate verursachen Teilchengrößeneinflüsse bei der Hydrierung von Alkenen auf Palladium

Abstract

Die Reaktionen linearer Alkene mit Metalloberflächen sind bereits anhand von unterschiedlich komplexen Modellkatalysatorsystemen studiert worden -von Einkristallen bis zu trägerfixierten Metallnanoteilchen auf geordneten Oxidfilmen.[

Acetylene and Ethylene Hydrogenation on Alumina Supported Pd-Ag Model Catalysts

“…Recently, our group has studied ethylene hydrogenation over Pd particles supported on a thin alumina film both at low pressures (with TPD) and high pressures (up to 1 bar, using gas chromatography analysis) [16][17][18]. Under both conditions, the ethylene hydrogenation reaction was found to be structure insensitive.…”

“…We have previously shown that the production of ethane from ethylene critically depends on the amounts of hydrogen residing in the sub-surface region of Pd particles [17,21]. In order to study this effect for hyd rogenation of acetylene, we adsorbed hydrogen on pure Pd particles at different temperatures (200 -300 K) followed by adsorption of acetylene at 100 K. Fig.…”

“…However, when the Pd particles are exposed below 200 K to the same amounts of H 2 , desorption emerges at much lower temperatures than on Pd(111) [17]. The low temperature (LT) state(s) can be attributed to the recombination of surface H species, which are more weakly bonded to the surface in the presence of sub-surface hydrogen.…”

“…The low temperature (LT) state(s) can be attributed to the recombination of surface H species, which are more weakly bonded to the surface in the presence of sub-surface hydrogen. The sub-surface hydrogen is available for the reaction on the particles due to their limited size in contrast to Pd crystals where hydrogen may migrate into the bulk far away from the surface [16,17,19,22,23]. Upon heating of the Pd particles, surface H species are re-populated by the H atoms from the sub-surface region, finally leading to the situation where sub-surface hydrogen is depleted and the desorption becomes similar to the case of adsorption at 300 K.…”

Model Systems in Heterogeneous Catalysis: Selectivity Studies at the Atomic Level

“…Here, we will discuss a few recent examples from the author's laboratory, i.e., methanol dehydrogenation on Pd nanoparticles [8,9], methanol oxidation on vanadia surfaces [10], ethene hydrogenation on Pd nanoparticles [11][12][13][14], and CO adsorption on Au atoms and clusters [15][16][17][18].…”