Nickel deposition on γ-Al 2O 3 model catalysts: An experimental and theoretical investigation

Abstract

Recently, surface modifications on a commercial Ni/γ-Al 2O 3 catalyst during the production of methane from synthesis gas were investigated by quasi in situ X-ray photoelectron spectroscopy (XPS) [I. Czekaj, F. Loviat, F. Raimondi, J. Wambach, S. Biollaz, A. Wokaun, Appl. Catal. A: Gen. 329 (2007) 68]. The conclusion was that the reactivity and the observed reaction mechanisms on the different Ni particles are influenced directly by both the size and the composition of the particles on the γ-Al 2O 3 support. In this investigation, Ni deposition and cluster growth on model catalyst samples (10 nm thick, polycrystalline γ-Al 2O 3 on Si(100)) were investigated by XPS. Several steps in the binding energy during Ni deposition indicate changes in the cluster growth. The molecular structure of the catalyst was investigated using Density Functional Theory calculations (StoBe) with a cluster model and non-local functional (RPBE) approach. An Al 15O 40H 35 cluster was selected to represent the γ-Al 2O 3(100) surface. Ni clusters of different size were cut from a Ni(100) surface and deposited on the Al 15O 40H 35 cluster in order to validate the deposition model determined by XPS.