Simulating the Complexities of Heterogeneous Catalysis with Model Systems: Case studies of SiO2 Supported Pt-Group Metals

Abstract

Model catalyst surfaces, consisting of vapordeposited metal nanoparticles supported on a planar oxide support, can help to link reactivity studies on well-defined single crystal surfaces with those conducted on high-surface area supported catalysts. When coupled with near atmospheric pressure kinetic and spectroscopic techniques, these well-defined model catalyst surfaces represent a useful approach to combine the power of surface analytical techniques with reactivity studies under relevant reaction conditions. Here, we review recent results of our investigations characterizing the physical and catalytic properties of Pt/SiO 2 and Rh/SiO 2 model catalyst surfaces. As will be discussed, the model catalyst approach can help simulate the complexities of catalytic reactions on supported catalysts, helping to provide insights into the role of particle size, particle morphology, and surface adsorbates in dictating the observed structure-sensitivity (activity and selectivity) during reactions at near atmospheric pressures.

Catalysis with Supported Size-selected Pt Clusters

“…Similar sized catalysts were investigated under near atmospheric pressures (in a reaction cell) and supported by UHV characterization. TOF and activation energies were extracted and the results were extrapolated to single crystal data, suggesting no size effects in 2 − 3 nm particles [92,19]. Catalysts synthesized by colloidal methods and tested in flow reactors, at elevated temperatures, support these findings [46,94] and the assumption of structure insensitivity.…”

“…PVD (Physical Vapor Deposition) [19,20] that motivate their use despite extreme experimental effort. Most important, the deposition of clusters formed in the gas phase allows for unpreceindependent size and coverage control dented control of size.…”

“…Other, (optical) techniques have been readily applied at higher pressures as well, e.g. IRRAS [195,19], S-SHG [109] or FEM [196]. On the other hand, a current trend in achieving insight at elevated pressures and more realistic conditions is the application of new characterization methods, such as micro-reactors new methods [197,198] or sensing devices, exploiting different physical properties [199,200,201,202].…”

“…On the other hand, a current trend in achieving insight at elevated pressures and more realistic conditions is the application of new characterization methods, such as micro-reactors new methods [197,198] or sensing devices, exploiting different physical properties [199,200,201,202]. 19 The complexity gap is covering the study of gas and mass transport phenomena, which additionally to materials and pressure gaps need to be considered [178]. 20 The first example was the calculation of the rate of ammonia formation under industrial conditions [176,177], based on well studied single-crystal surface reactions [74,181,6].…”

Recent developments in the application of nanomaterials to understanding molecular level processes in cobalt catalysed Fischer–Tropsch synthesis

“…The use of nanotechnology to develop advanced materials for use as model catalysts has been a key recent development in studying heterogeneous catalysis. 14,15,16,17 The advantage gained is that numerous model structures with good control over metal particle size, shape, composition and metal oxide structure and porosity can be made. 18 The uniformity that can be obtained is invaluable in two ways.…”