Abstract
Nanostructured gold is an intriguing system for heterogeneous catalysis at low temperature. Its activity is related to choice of support selection, particle-support interaction, and especially the particle size. Here, we investigate the possibility of controlling the size of Au clusters (nanoparticles) in the novel Matrix Assembly Cluster Source (MACS), a solvent-free nanoparticle source with potential for scale-up to the gram level. The novelty of the MACS is the idea of making clusters by sputtering a pre-condensed matrix of metal atoms embedded in a condensed non-reactive gas, e.g., Ar. This concept, introduced in 2016, has already proved deposition rates several orders of magnitude higher than conventional cluster beam routes. Such scale-up in the cluster production rate is crucial for industrial research on nanocatalysis under realistic reaction condition. Here, we report a systematic study of how Au metal loading in the matrix affects the size distribution of clusters generated. Furthermore, the obtained dependence of cluster size on deposition time provides clear confirmation of cluster formation inside the matrix by ion irradiation, rather than by aggregation of atoms on the TEM support after deposition.
Highlights
The present work is motivated by the fact that the active sites in heterogeneous catalysis are frequently supported nanoparticles
The size of the clusters was derived through atom counting method, using as reference the highangular annular dark-field (HAADF)-STEM intensity of size-selected Au923 clusters, prepared using a magnetron sputtering cluster source with mass resolution of ± 2.5%
We show that the size of Au clusters generated by the Matrix Assembly Cluster Source (MACS) can be tuned by the metal concentration in the MACS matrix
Summary
The present work is motivated by the fact that the active sites in heterogeneous catalysis are frequently supported nanoparticles. Among the available techniques which generate “pre-prepared” nanoparticles, cluster beam deposition is an emerging technology able to produce films of clusters with tunable size and composition (Palmer et al 2018; Grammatikopoulos et al 2016; Ayodele et al 2020) Since it does not need solvent for the generation and stabilization of the nanoparticles, it obeys the green chemistry 12 principles (Anastas and Warner 1998) and represents an appealing new method of preparation of model catalysts. The Matrix Assembly Cluster Source (MACS) addresses this issue of production rate (Palmer et al 2016) and is based on a new principle for the generation of clusters: ion beam impact on a matrix of metal atoms in a non-reactive gas condensed on a cryogenically cooled support. The HAADF images were acquired with inner and outer collection angles of 62 mrad and 164 mrad (camera length 10 cm)
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