CO Oxidation Catalyzed by Oxide-Supported Au₂₅(SR)₁₈ Nanoclusters and Identification of Perimeter Sites as Active Centers

Abstract

In this work, we explore the catalytic application of atomically monodisperse, thiolate-protected Au 25 (SR) 18 (where R = CH 2 CH 2 Ph) nanoclusters supported on oxides for CO oxidation.The solution phase nanoclusters were directly deposited onto various oxide supports (including TiO 2 , CeO 2 , and Fe 2 O 3 ), and the as-prepared catalysts were evaluated for the CO oxidation reaction in a fixed bed reactor. The supports exhibited a strong effect, and the Au 25 (SR) 18 /CeO 2 catalyst was found to be much more active than the others. Interestingly, O 2 pretreatment of the catalyst at 150 °C for 1.5 h significantly enhanced the catalytic activity. Since this pretreatment temperature is well below the thiolate desorption temperature (∼200 °C), the thiolate ligands should remain on the Au 25 cluster surface, indicating that the CO oxidation reaction is catalyzed by intact Au 25 (SR) 18 /CeO 2 . We further found that increasing the O 2 pretreatment temperature to 250 °C (above the thiolate desorption temperature) did not lead to any further increase in activity at all reaction temperatures from room temperature to 100 °C. These results are in striking contrast with the common thought that surface thiolates must be removed ; as is often done in the literature work ; before the catalyst can exert high catalytic activity. The 150 °C O 2pretreated Au 25 (SR) 18 /CeO 2 catalyst offers ∼94% CO conversion at 80 °C and ∼100% conversion at 100 °C. The effect of water vapor on the catalytic performance is also investigated. Our results imply that the perimeter sites of the interface of Au 25 (SR) 18 /CeO 2 should be the active centers.The intact structure of the Au 25 (SR) 18 catalyst in the CO oxidation process allows one to gain mechanistic insight into the catalytic reaction.

Isolation and Tandem Mass Spectrometric Identification of a Stable Monolayer Protected Silver–Palladium Alloy Cluster

“…The crude product upon chromatographic analyses under optimized conditions gave three distinct clusters with unique optical features. One of these exhibits a molecular peak centered at m/z 2839, in its negative ion mass spectrum assigned to Ag 5 Pd 4 (SePh) 12 − , having an exact match with the corresponding calculated spectrum. Tandem mass spectrometry of the molecular ion peak up to MS 9 was performed.…”

“…Outer electron count of the Ag 5 Pd 4 (SePh) 12 system would suggest a 33 electron species (taking s 1 and d 10 valence shells for Ag and Pd, respectively, and subtracting one electron each for the ligands, which form the selenolates, and the entity as a whole may be stabilized by a negative change, making the system a closed shell. This may be the reason for the larger intensity of the negative ion.…”

“…The crude cluster was purified using HPLC, which gave three different clusters with characteristic optical absorption spectra. ESI MS data suggest that only cluster 2 shows interesting features for which the molecular ion peak appeared at m/z 2839, assigned as [Ag 5 Pd 4 (SePh) 12 ] − . Systematic MS/MS was carried out for the molecular ion peak as well as other fragments.…”

Fluorescent Gold Nanoclusters: Promising Fluorescent Probes for Sensors and Bioimaging

“…Jin's group explored the catalytic application of thiolate-protected Au 25 (SR) 18 (R = CH 2 CH 2 Ph) in the CO oxidation reaction. They reasoned that the great catalytic performance resulted from the low-coordinate Au atoms on the exterior shell of AuNCs which could provide a favorable environment for the adsorption and activation of certain reactants [27]. 6 nanoclusters were capable of catalyzing CO oxidation reaction [28].…”

Active metal (cadmium) doping enhanced the stability of inert metal (gold) nanocluster under O2 atmosphere and the catalysis activity of benzyl alcohol oxidation

“…In the past few years, significant advances have been made in the synthesis and property studies of these doping nanoclusters [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Among homogold nanoclusters, Au 25 (SR) 18 nanocluster has been well studied due to its stable structure among three different charges (−1/0/+1) [22][23][24][25][26], which led to the exploration of a wide range of catalytic pathways facilitated by Au 25 for organic reactions, such as oxidation [27][28][29], hydrogenation [30][31][32], electronic transfer reactions [26,33], and electrocatalysis [34,35]. Recent research implies that doping foreign atoms into this 25 noble metal system can largely affect the stability and the catalytic activity compared to the homogold counterpart [7][8][9][10][17][18][19].…”