Atomically Well Defined Thiolate Gold Nanoclusters for Heterogeneous Catalysis
Résumé
Gold nanoparticles exhibit a catalytic activity in many chemical processes.1 Most of the reactions are size-dependant, i. e. the specific activity depends on the average gold particle size. Generally, the activity increases when the particle size decreases, with a marked increase below 5 nm, which strongly supports the role of surface gold atoms in the reactions. But for sub-2 nm particles, the origin of the catalytic power is still unclear and under intense debate. Fundamental investigations on the structure-catalytic activity relationships still lag behind, partly due to the polydispersity issue of gold nanoparticles. Indeed, polydisperse particles obscure the interesting size-dependent catalytic activity of nanogold and preclude an in-depth understanding of the origin of this size dependence. Recently, atomically well defined thiolate-capped Au nanoclusters (denoted as Aun(SR)m) have been successfully isolated and their catalytic properties have been demonstrated.2 These monodispersed functionalized clusters, with gold core between less than 1 nm and more than 2 nm, hold promises as a new generation of catalysts. More importantly, these nanoclusters permit in-depth studies on the subtle correlation of structure and catalytic activity, since they are well defined and their crystallographic structures start to be solved.3 To investigate the influence of the size, the type of ligands at the surface and also the support effect, different nanoclusters have been synthesized. New clusters made of 4-aminothiophenol (HSPhNH2) have been synthesized, such as Au25(SPhNH2)17, and fully characterized by mass spectrometry, X-ray diffraction and XPS.4 Moreover these clusters exhibit absorption bands and paramagnetic behaviour related to their molecular state. Catalytic activity for oxidation of alkene and alcohol derivatives of these colloidal or supported clusters were investigated and compared to the commonly used Aun(SCH2CH2Ph)m nanoclusters. At the opposite of the bare gold nanoparticles, the presence of the ligands around the clusters leads to a much better selectivity of the product. (1) Hashmi, A. S. K.; Hutchings, G. J. Angew. Chem.-Int. Edit. 2006, 45, 7896. (2) Jin, R. C.; Zhu, Y.; Qian, H. Chem. Eur. J. 2011, 17, 6584. (3) Zhu, Y.; Qian, H. F.; Zhu, M. Z.; Jin, R. C. Adv. Mater. 2010, 22, 1915. (4) Lavenn, C.; Albrieux, F.; Bergeret, G.; Chiriac, R.; Delichčre, P.; Tuel, A.; Demessence, A. Nanoscale DOI: 10.1039/C2NR32367B.