Efficient One-Pot Synthesis and pH-Dependent Tuning of Photoluminescence and Stability of Au18(SC2H4CO2H)14 Cluster

Ramakrishna Itteboina, U. Divya Madhuri, Partha Ghosal, Monica Kannan, Tapan Kumar Sau*, Tatsuya Tsukuda, and Shweta Bhardwaj
J. Phys. Chem. A, Just Accepted Manuscript

Developing efficient ways to control the nanocluster properties and synthesize atomically-precise metal nanoclusters are the foremost goals in the field of metal nanocluster research. In this article, we demonstrate that the direct synthesis of atomically-precise, hydrophilic metal nanoclusters as well as tuning of their properties can be achieved by an appropriate selection of reactants, binding ligand, and their proportions. Thus a facile, single-step method has been developed for the direct synthesis of Au18(SC2H4CO2H)14 nanocluster in an aqueous medium under ambient conditions. The synthesis does not require any pH or temperature control and post-synthesis size-separation step. The use of a hydrophilic, bifunctional short carbon-chain capping ligand, HSC2H4CO2H, allows tuning of cluster properties such as the photoluminescence and stability in an aqueous medium via the variation of pH of the cluster solution. By using a phase transfer catalyst, the nanoclusters can also be transferred into toluene solvent which further enhances the nanocluster photoluminescence. The formation, composition, and purity of the product clusters have been characterized by using a number of methods such as the polyacrylamide gel electrophoresis (PAGE), UV-visible and FTIR spectroscopies, transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Gold nanoclusters with properties such as water solubility, water-to-organic phase-transfer ability and tunable stability and photoluminescence are promising for various studies and applications. The work reveals a few principles that can be helpful in the development of a general toolbox for the rational design of size-selective synthesis and properties tuning of the metal nanoclusters.

Dynamic Behavior of Rh Species of Rh/Al2O3 Model Catalyst During Three-Way Catalytic Reaction — An Operando XAS Study

Hiroyuki Asakura, Saburo Hosokawa, Toshiaki Ina, Kazuo Kato, Kiyofumi Nitta, Kei Uera, Tomoya Uruga, Hiroki Miura, Tetsuya Shishido, Jun-ya Ohyama, Atsushi Satsuma, Katsutoshi Sato, Akira Yamamoto, Satoshi Hinokuma, Hiroshi Yoshida, Masato Machida, Seiji Yamazoe, Tatsuya Tsukuda, Kentaro Teramura, and Tsunehiro Tanaka*
J. Am. Chem. Soc. 140, 176-184 (2018).

The dynamic behavior of Rh species in 1 wt% Rh/Al2O3 catalyst during the three-way catalytic reaction was examined using a micro gas chromatograph, a NOx meter, a quadrupole mass spectrometer, and time-resolved quick X-ray absorption spectroscopy (XAS) measurements at a public beamline for XAS, BL01B1 at SPring-8, operando. The combined data suggest different surface rearrangement behavior, random reduction processes, and autocatalytic oxidation processes of Rh species when the gas is switched from a reductive to an oxidative atmosphere and vice versa. This study demonstrates an implementation of a powerful operando XAS system for heterogeneous catalytic reactions and its importance for understanding the dynamic behavior of active metal species of catalysts.

Doping a Single Palladium Atom into Gold Superatoms Stabilized by PVP: Emergence of Hydrogenation Catalysis

Shun Hayashi, Ryo Ishida, Shingo Hasegawa, Seiji Yamazoe, and Tatsuya Tsukuda*
Topics in Catalysis, Just Accepted Manuscript

It is known that small gold clusters (average diameter: ~1.2 nm) stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP) exhibit size-specific catalysis in aerobic oxidation reactions. A recent matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) study of Au:PVP revealed that Au clusters with the magic sizes of 34 and 43 were preferentially produced. Here, we reported how the doping of palladium (Pd) into Au:PVP affects the catalytic performance. MALDI-MS analysis of Pd-doped Au:PVP showed that a single Pd atom was selectively doped by co-reduction of Au and Pd precursor ions and that PdAu33 and PdAu43 were produced as the dominant species. Extended X-ray absorption fine structure (EXAFS) analysis indicated that a Pd atom was located at the exposed surface of the Au:PVP clusters. It was found that single Pd atom doping enhanced the catalytic activity for aerobic oxidation of benzyl alcohol and provided hydrogenation catalysis in a chemoselective manner to the C=C bonds over the C=O bonds.

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