Abstract
It is well known that particle size plays an important role in catalytic activity although the reason(s) why significant changes in activity are observed to occur with small changes in size are not well understood. The presence of particular facets, metal-support interactions, and redox state etc., are also capable of playing a role. The difficulty in realising which features are pertinent in a catalytic process stems from issues regarding sample complexity in typical heterogeneous catalysts, as well as technical challenges with instruments used to investigate samples in terms of their sensitivity and capability to distinguish between a specific vs. ensemble response in catalytically active vs. spectator species. We show here how the combination of using a synthesis method which achieves a discrete dispersion of metal Pd nanoparticles with a very narrow particle size distribution (σ ~ 1 nm) in combination with nano-beam X-ray spectroscopy allows us to follow the changes in redox state with time. Importantly, the data are obtained in one example, from an illuminating spot containing ca. 20 nanoparticles with an extremely small size distribution.
Highlights
Precious metal nanoparticles comprising Pt, Au, Pd etc. supported on light metal oxides (i.e. Al2O3, SiO2, TiO2) form the basis of many types of critical industrial heterogeneous catalyst systems
In order to gain a working insight into the nature of the active component in the system, research efforts have been directed towards studying catalysts using nanoparticle sensitive X-ray synchrotron based techniques such as XAS (X-ray Absorption Spectroscopy) amongst others [1]
First we discuss the characterisation of the stock solutions in terms of the size of the Pd nanoparticles that the synthesis approach yields, before discussing how this particle size is maintained when the particles are subsequently transferred to high surface area Si3N4 powders or SiNx reactor windows
Summary
Precious metal nanoparticles comprising Pt, Au, Pd etc. supported on light metal oxides (i.e. Al2O3, SiO2, TiO2) form the basis of many types of critical industrial heterogeneous catalyst systems. Precious metal nanoparticles comprising Pt, Au, Pd etc. Numerous examples exist in the literature which testify that the size and/or shape of the nanoparticle is an important parameter influencing catalytic activity [2,3,4,5,6]. It is well known that nanoparticles actively respond to their environment in situ, often changing shape so as to maximize, for example, the contact area of a particular surface, e.g. the (1 1 1) surface [7]. In the majority of these studies the preparation methods used to make these catalysts result in nanoparticles with large particle size distributions (standard deviation, σ > 1 nm), essentially masking the importance of a particular particle size or shape on activity.
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