Supports and Modified Nano-particles in Designing Model Catalysts

Abstract

In order to design catalytic materials, we need to understand the essential causes for material properties resulting from its composite nature. In this paper we discuss two, at first sight, diverse aspects: a) the effect of the oxide-metal interface on metal-nanoparticle properties and b) the consequences of metal particle modification after activation on the selectivity of hydrogenation reactions. However, those two aspects are intimately linked. The metal-nanoparticles electronic structure changes at the interface as a catalyst is brought to different reaction temperatures due to morphological modifications in the metal and, as we will discuss, those changes the chemistry leading to changes in the reaction path. As the morphology of the particle varies, facets of different orientation and size are exposed which may lead to a change in surface chemistry as well. We use two specific reactions to address those issues in some detail. To the best of our knowledge the present paper reports the first observations of this kind for well-defined model systems. The changes of the electronic structure of Au nanoparticles due to their size and interaction with a supporting oxide are revealed as a function of temperature using CO2 activation as a probe. The presence of spectator species (oxopropyl) as formed during an activation step of acrolein hydrogenation, strongly controls the selectivity of the reaction towards hydrogenation of the unsaturated C-O vs. the C-C bond on Pd(111) when compared with oxide supported Pd nanoparticles.