(101g) Supported Gold Clusters with Modulated Environment for Catalysis

There exists a high level of interest in noble metal clusters due to their promising applications in diverse fields, from catalysis to biomedical applications. Among all of the noble metals, gold holds a distinctive place, as it possesses a unique combination of different chemical and physical properties at the nanoscale, as well as at the macroscale. Many techniques have been reported to synthesize monodisperse gold clusters (< 2nm in size) with different types of functional groups employed to stabilise them. [1] The major advantage of small clusters for catalytic applications is the high surface area to volume ratio, which results in a high fraction of atoms on their surface, an essential element in heterogeneous catalysis. Along with the size of the metal clusters, the environment around the metal clusters’ active sites also plays an important role. As an example, enzymes, which are nature’s catalysts, use functional groups around the active site to modulate the environment for catalytic reactions. Taking inspiration from enzymatic structures, we can tune the environment around gold by changing the stabilizing ligands which, consequently, modulates the steric, electronic, and catalytic properties of the gold clusters. [2-3]

Herein, we present a simple, one-pot methodology to synthesise very stable, atomically precise gold clusters of ~ 1.2 nm average core diameter. [4] The particle size was characterized using UV/Vis spectroscopy and HAADF-STEM. In addition to batch synthesis, this synthesis is also demonstrated using a microfluidic continuous flow system. The continuous flow system has various advantages over the batch system, such as controlled mixing and a narrow residence time distribution. Different gold (I) precursors of varying steric hindrance have been employed to tune the final size of the gold clusters. A relationship has been developed correlating the steric hindrance around the metal and the final size of nanoparticles. Further, these gold clusters are successfully immobilized onto different metal oxide supports, like TiO₂ and SiO₂, without any alteration in the final size of the immobilized gold clusters. The catalytic activity of these supported gold clusters in the conversion of benzyl alcohol to benzaldehyde will be demonstrated. Initial results of these catalysts show high selectivity towards benzaldehyde. The effect of the ligand on the catalytic activity of these gold clusters is also elucidated.

[1] M. Haruta, Chem. Rec. 3 (2003) 75-87.
[2] P. Trogadas, M. M. Nigra, M.-O. Coppens, New J. Chem. 40 (2016), 4016-4026.
[3] M. M. Nigra, A. J. Yeh, A. Okrut, A. G. DiPasquale, S. W. Yeh, A. Solovyov, A. Katz, Dalton Trans. 42 (2013) 12762-12771.
[4] N. Kapil, M. M. Nigra, M.-O. Coppens 2018, in preparation.