Abstract
Abstract Using oxide supported atomically precise gold nanoclusters is an emerging field in heterogeneous catalysis. Such well-defined nanocatalysts represent a rather new model system enabling fundamental insights in catalytic reactions. In the present work, the stability of Au25 and Au144 clusters, supported either on TiO2 or SiO2, was examined upon thermal air pretreatment and, for the first time, upon liquid phase oxidation reaction. A pronounced influence of the support (TiO2 vs. SiO2) and cluster size (Au25 vs. Au144) was revealed by XAS, DRS and STEM. Upon pretreatment, Au144 was more stable which may be related to its specific cluster core structure and staple configuration. The catalytic properties in liquid phase cyclohexane oxidation were clearly size dependent, with Au144 yielding higher TOF values, particularly in the case of SiO2 supported catalysts. However, with respect to selectivity, TiO2 supported catalysts led to higher KA production than SiO2 supported ones. This can be explained by the different reaction pathways, as observed by in situ ATR. HERFD-XAS measurements of Au144/TiO2 catalysts revealed a pronounced cluster structure modification towards bulk gold during the reaction, in contrast to a high stability of Au144/SiO2. This study demonstrates the important role the support material has on the reactivity and stability of gold nanoclusters, which is key for their catalytic function.
Highlights
Gold catalysts were generally considered to be inactive until the 1980s, when Haruta [1] reported high activity of Au particles smaller than 5 nm, supported on 3d transition metal oxides
The purity of the synthesized Au25(SC2H4Ph)18 and Au144(SC2H4Ph)60 cluster solutions was confirmed by UV–vis and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (Fig. S1) [45,46]
This may be related to the different cluster core structures, with the hollow icosahedral Au114 core of Au144 being more stable than the Au13 icosahedral core of Au25
Summary
Gold catalysts were generally considered to be inactive until the 1980s, when Haruta [1] reported high activity of Au particles smaller than 5 nm, supported on 3d transition metal oxides. Previous studies revealed a strong dependence of the catalytic properties on the particle size and stability of gold nanoclusters, e.g. in oxidation reactions. Carbon supported Aun(SG)m clusters (n = 5, 10, 18, 25, 39, ∼ 85) (G = glutathione), after ligand removal, were all active in the aerobic oxidation of cyclohexane to cyclohexanol and cyclohexanone, but with a volcano-type dependence with a maximum at n = 39 [17] This clearly shows how a difference in cluster size of several atoms affects the catalytic activity. The influence of the ligand coverage around the gold core on the activity in cyclohexane oxidation was studied by Zhang et al [30] using Au38(SR) clusters supported on CeO2 and Al2O3. Relevant differences were observed between both clusters and supports, in terms of stability and reactivity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
