Size-Dependent Oxidation Mechanism of Supported Pd Nanoparticles

摘要

Nanometer-sized metal particles on oxide surfaces have numerous technological applications, particularly in the field of heterogeneous catalysis.[1], [2] Many catalysts applied in the chemical industry for emission control or in energy technology are based on finely dispersed noble-metal aggregates on oxides. But is the surface of these metal aggregates truly metallic under reaction conditions? This seemingly elementary question turns out to be very difficult to answer. The reason is that the influence of the reactant atmosphere on the surface structure, morphology, and composition may be rather complex. Especially in the case of oxygen-containing environments, the situation turns out to be particularly intricate. Many different oxygen species may be present even on simple single-crystal surfaces, including various types of chemisorbed oxygen (i.e. oxygen adsorbed above the first atomic layer of the metal), subsurface oxygen (i.e. oxygen incorporated into the first layers of metal atoms), thin surface oxides (i.e. very thin structures consisting of oxygen and metal-ion layers), and bulk oxides.[3]-[16] The puzzling role of these multiple species in reaction kinetics is a major challenge for microscopic studies in catalysis, and the related questions are currently the subject of intensive discussion (see e.g.[17]-[19]).