Following the Thermal Activation of Au₂₅(SR)₁₈ Clusters for Catalysis by X-ray Absorption Spectroscopy

Abstract

We show the thermal activation of phenylethanethiolate (L = SC 8 H 9 ) and hexanethiolate (L = SC 6 H 13 )A u 25 L 18 monolayer protected clusters (MPCs) on carbon black supports, followed by characterization with extended Xray absorption fine structure (EXAFS) spectroscopy and transmission electron microscopy (TEM). EXAFS analysis shows that the thiolate stabilizers can be partially removed from the surface under mild heating conditions without significant changes in the cluster size. The resulting clusters are shown to be catalytically active for the reduction catalysis of 4-nitrophenol. EXAFS and TEM data show that thermal treatment under air at 200°C leads to nearly complete removal of all of the thiolate stabilizers with little to no growth in cluster size, while cluster sintering was seen at higher calcination temperatures. The maximum catalytic activity for Au 25 (SC 8 H 9 ) 18 MPCs was seen at 250°C activation conditions. These results are consistent with results reported earlier for Au 25 (SR) 18 clusters on ceria by Jin et al., who suggested that cluster integrity was maintained during mild activation conditions. Here, EXAFS data unambiguously show that while the cluster size does not grow significantly, such mild heating conditions do lead to nearly complete removal of the thiolate stabilizers.

Fuel mediated solution combustion synthesis of ZnO supported gold clusters and nanoparticles and their catalytic activity and in vitro cytotoxicity

“…Similar studies with Au/Ag clusters have been reported by other earlier workers. 29,46,47 Our experiments …”

Sub-nanometer sized Cu6(GSH)3 clusters: one-step synthesis and electrochemical detection of glucose

“…23,24 When metal nanoclusters are used as catalysts, appropriate supports are usually needed to not only improve their dispersity but also enhance the stability. Among the materials, carbon and transition metal oxides are most widely used as supports.…”

Bonding properties of thiolate-protected gold nanoclusters and structural analogs from X-ray absorption spectroscopy

“…Such structural information is crucial for identifying and further understanding the catalytically active locations on the surface of the metal NP or NC. A study by Shivhare et al demonstrated that partially or completely removing the protecting ligands from alkanethiolate-protected Au 25 NCs (supported on carbon powder) by calcination increased the catalytic reduction of 4-nitrophenol [51]. Au L 3 -edge EXAFS spectra for Au 25 (SC 8 H 9 ) 18 and Au 25 (SC 6 H 13 ) 18 were collected before thermal treatment and fitted using four shells to confirm the core and surface local structure of the NC samples.…”