The support effect on the size and catalytic activity of thiolated Au₂₅nanoclusters as precatalysts

Abstract

In this study, 6-mercaptohexanoic (MHA) protected Au25(MHA)18 nanoclusters (or thiolated Au NCs) deposited on various inorganic supports, including hydroxyapatite (HAP), TiO2 (Degussa P25), activated carbon (AC), pyrolyzed graphene oxide (PGO), and fumed SiO2 were prepared via a conventional impregnation method. Following that, calcination under a N2 stream was conducted to produce surface ligand free, highly dispersed Au NCs catalysts. The effects of supports on the size and catalytic activity of Au NCs were systematically investigated. No obvious size growth was observed for Au NCs on HAP and P25 after thermally induced ligand removal, due to the strong interaction between the metal and the supports. However, severe aggregations of Au NCs were seen after thermal treatment on three other supports, including AC, PGO, and SiO2. The removal of surface thiol ligands from the Au NCs is crucial to catalyze nitrobenzene hydrogenation, where only calcined Au/HAP and Au/P25 exhibited good catalytic activity. On the other hand, all the supported Au NCs were active for the styrene oxidation, where Au/HAP exhibited the best catalytic performance. Altogether, both the size effect and metal-support interaction are crucial for the design of supported Au NCs as efficient catalysts for targeted reactions.

Engineering Surface Ligands of Noble Metal Nanocatalysts in Tuning the Product Selectivity

“…The capping effect can exist at both interfaces of metal-reactants and metal-support. Using CO oxidation as a model reaction, Wu et al studied the catalytic activity of Au 25 (SR) 18 supported on CeO 2 [75]. A strong site-blocking effect was found on fully covered Au nanoclusters where the CO adsorption was completely suppressed.…”

“…In the presence of dodecanethiol ligands, partially covered surface reduced the catalytic ability of Au 25 nanocatalysts by restricting the adsorption of reactants and intermediate states (including benzaldehyde). Thus, only partially oxidized benzaldehyde was obtained for dodecanethiol-coated Au 25 . In the absence of surface ligands, a high selectivity for a fully oxidized product of benzoic acid and ester was observed.…”

“…In the presence of excess surface ligands (essentially necessary during the wet-chemical synthesis), ligands can form a densely packed self-assembled monolayer (SAM) in the thickness of 0.5-3 nm by maximizing van der Waals interactions of alkyl chains [18]. The surface ligands are demonstrated to be detrimental to the catalytic activity in many examples [20][21][22][23][24][25][26][27]. The formation of SAMs is often considered to block the surface accessibility, leading to a decrease in the accessibility of catalytic sites [20,23], although there are many reported examples showing that surface ligands do not depress catalytic activity of metal NPs [28][29][30][31].…”

AgAu Nanotubes: Investigating the Effect of Surface Morphologies and Optical Properties over Applications in Catalysis and Photocatalysis

“…16,17 In addition to properties in sensing (enhanced spectroscopies), the LSPR excitation can also be put to work towards the promotion and/or enhancement of chemical processes, the so-called plasmonic catalysis that has emerged as a new frontier in the field of photocatalysis. [18][19][20] Nanoparticles based on noble metals have also been widely employed in the field of heterogeneous catalysis and electrocatalysis due to their good stability and catalytic activities towards a wealth of transformations including oxidations, 15,[21][22][23] reductions, 9,24 coupling reactions, [25][26][27][28] among others. 8,[29][30][31] In these applications, it has been established that the precise control over their morphological and optical properties is a promising strategy to enhance/ optimize their performances.…”

In situ thermolysis of Pt-carbonyl complex to form supported clean Pt nanoclusters with enhanced catalytic performance

“…AN is typically prepared by the hydrogenation of nitrobenzene (NB) in the liquid or vapor phase, and the latter is usually performed at 473 K over copper-based catalysts [1], which often suffers from low selectivity and poison resistance [2]. Noble metal (such as Pd, Pt, Ru) catalysts have been developed and demonstrated to show good performance in the hydrogenation of NB in the liquid-phase [3][4][5][6]. In such systems, harsh reaction conditions, e.g., higher system temperature and pressure are commonly required [7][8][9][10][11].…”