Jiahui Huang

Gas-phase propene epoxidation over coinage metal catalysts

Propene oxide (PO) is a very important bulk chemical and is produced on a scale of about 7.5 million tons per year. In industry, PO is produced via multiple reaction steps in the liquid phase, using hazardous chlorine or costly organic hydroperoxides as oxidants. Accordingly, development of a simple and green process to produce PO has been desired. This paper presents an overview of one-step propene epoxidation in the gas phase over coinage metal catalysts with a mixture of O2 and H2 or with molecular O2 alone as oxidant. Silver (Ag) and gold (Au) catalysts can catalyze propene epoxidation with a mixture of O2 and H2, with high selectivity, whereas copper (Cu) catalysts cannot. In this reaction Au catalysts are much more active than Ag catalysts. All the coinage metals can catalyze propene epoxidation by molecular O2, but with selectivity usually below 60%. The valence states of Cu species and the sizes of Ag particles and Au particles are of crucial importance in PO synthesis.

Classical strong metal–support interactions between gold nanoparticles and titanium dioxide

The classical strong metal–support interaction between TiO2 and IB metals was demonstrated. Supported metal catalysts play a central role in the modern chemical industry but often exhibit poor on-stream stability. The strong metal–support interaction (SMSI) offers a route to control the structural properties of supported metals and, hence, their reactivity and stability. Conventional wisdom holds that supported Au cannot manifest a classical SMSI, which is characterized by reversible metal encapsulation by the support upon high-temperature redox treatments. We demonstrate a classical SMSI for Au/TiO2, evidenced by suppression of CO adsorption, electron transfer from TiO2 to Au nanoparticles, and gold encapsulation by a TiOx overlayer following high-temperature reduction (reversed by subsequent oxidation), akin to that observed for titania-supported platinum group metals. In the SMSI state, Au/TiO2 exhibits markedly improved stability toward CO oxidation. The SMSI extends to Au supported over other reducible oxides (Fe3O4 and CeO2) and other group IB metals (Cu and Ag) over titania. This discovery highlights the general nature of the classical SMSI and unlocks the development of thermochemically stable IB metal catalysts.

Efficient Aerobic Oxidation of Glucose to Gluconic Acid over Activated Carbon‐Supported Gold Clusters

The catalytic performance of the atomically precise gold cluster-Au38 (PET)24 (PET=2-phenylethanethiolate), immobilized on activated carbon (AC), was investigated for the aerobic oxidation of glucose to gluconic acid. The Au38 (PET)24 /AC-120 catalysts, annealed at 120 °C in air, exhibited high catalytic activity and significantly better performance than the corresponding catalysts Au38 /AC-150 and Au38 /AC-300 (treated at 150 and 300 °C to remove the protecting thiolate ligands). The high activity of the robust Au cluster was a result of the partial ligand removal, providing catalytically active sites, which were evidenced by TEM, X-ray photoelectron spectroscopy, thermogravimetric analysis, and Fourier-transform IR spectroscopy. Au38 (PET)24 /AC-120 also showed excellent recyclability (up to seven cycles). The turnover frequency for the Au38 (PET)24 /AC-120 catalyst was 5440 h-1 , which is higher than for the Pd/AC, Pd-Bi/AC, and Au/AC under identical reaction conditions. This new ultra-small gold nanomaterial is expected to find wide application in other catalytic oxidations.

One-pot synthesis of Au144(SCH2Ph)60 nanoclusters and their catalytic application

Here, we report the one-pot synthesis of atomically precise gold nanoclusters – Au144(SCH2Ph)60 with moderate efficiency (ca. 20% yield based on HAuCl4). The Au144(SCH2Ph)60 nanoclusters are obtained from the polydispersed Aun(SG)m nanoclusters in the presence of excess H–SCH2Ph ligands via a combination of “ligand-exchange” and “size-focusing” processes. The as-obtained Au144(SCH2Ph)60 nanoclusters are well determined by UV-vis spectroscopy and electrospray ionization (ESI) mass spectrometry, and in conjunction with matrix-assisted laser desorption ionization (MALDI) mass spectrometry and thermal gravimetric analysis (TGA). The purity of the Au144(SCH2Ph)60 nanoclusters is further characterized by size exclusion chromatography (SEC) and elemental analysis. The powder X-ray diffraction (PXRD) analysis implies that the Au144(SCH2Ph)60 nanoclusters do not adopt the face-centered cubic (fcc) structure, as the diffraction angle (2θ = 50.5°) is only observed in the Au144(SCH2Ph)60 nanoclusters. Further, the Au144(SCH2Ph)60/TiO2 catalyst exhibits excellent catalytic performance (92% conversion of methyl phenyl sulfide with 99% selectivity for sulfoxide) in the selective sulfoxidation; size-dependence of the gold nanocluster catalyst is observed in the catalytic reactions: Au144(SCH2Ph)60 > Au99(SPh)42 > Au38(SCH2CH2Ph)24 > Au25(SCH2CH2Ph)18.

Highly efficient iron phthalocyanine based porous carbon electrocatalysts for the oxygen reduction reaction

Porous carbon (PC) materials with a large surface area and uniform pore sizes have been used as novel electrocatalysts to catalyze the oxygen reduction reaction (ORR). In this work, iron phthalocyanine (FePc) and magnesium oxide (MgO) were used as the precursors and hard-template, respectively, to fabricate FePc-based porous carbon non-noble metal electrocatalysts (NNMEs). The prepared FePc-based porous carbon electrocatalysts possess a high surface area of 555 m2 g−1 and a dual mesoporous structure with mean pore sizes of 3.6 nm and 32 nm, and display comparable ORR activity but superior durability than a commercial Pt/C electrocatalyst in alkaline solution. The excellent catalytic performance of FePc-based porous carbon electrocatalysts may be attributed to the large surface area, high density of iron based nano-particles (NPs) encapsulated in carbon layers and high content of doped nitrogen species.

Highly efficient electrocatalysts with CoO/CoFe2O4 composites embedded within N-doped porous carbon materials prepared by hard-template method for oxygen reduction reaction

Low-cost dual transition metal (Fe and Co) based non-noble metal electrocatalysts (NNMEs) have been explored to enhance the oxygen reduction reaction (ORR) performance in both alkaline and acidic solution. In this work, novel NNMEs derived from iron, cobalt and N-doped porous carbon materials (FeCo/NPC) were fabricated with magnesium oxide (MgO) as the hard-template. By optimizing the pyrolysis temperature (600 to 1000 °C) and the molar ratio of Fe to Co (Co, FeCo3, FeCo, Fe3Co, Fe), the highly active electrocatalyst FeCo/NPC (900) for ORR in alkaline solution was prepared, which possessed a large surface area of 958 m2 g−1. The onset potential (Eonset) and half-wave potential (E1/2) of FeCo/NPC (900) were 0.934 V and 0.865 V, respectively, comparable to the best values of NNMEs reported so far in ORR tests under alkaline conditions. Additionally, FeCo/NPC (900) exhibited better electrocatalytic properties than commercial Pt/C in terms of durability and the tolerance to methanol in alkaline media.

Controlled synthesis of pure Au25(2-Nap)18 and Au36(2-Nap)24 nanoclusters from 2-(diphenylphosphino)pyridine protected Au nanoclusters

The controlled synthesis of pure Au25(2-Nap)18 and Au36(2-Nap)24 nanoclusters were achieved via etching 2-(diphenylphosphino)-pyridine protected polydispersed Au nanoclusters with a mass of 1 to 3 kDa. Au25(2-Nap)18 was obtained at the etching temperature of 80 °C, while Au36(2-Nap)24 was synthesized at the etching temperature of 50 °C. This demonstrates that the simple adjustment of the etching temperatures can realize the controlled synthesis of different atomically precise Au nanoclusters.

Structural isomer and high-yield of Pt1Ag28 nanocluster via one-pot chemical wet method

In order to understand the structure–property correlation and explore the application of metal nanoclusters, it is important and intriguing to determine their crystal structure and obtain high-yield. At the same time, this is also a challenge in nanoscience and technology. Here, we report the highly efficient synthesis of Pt1Ag28 nanocluster via one-pot chemical wet method. The crystal structure of Pt1Ag28 nanocluster was determined by X-ray crystallography to be a face centered cubic (FCC) kernel. This novel structure is the structural isomerization of Pt1Ag28 nanocluster reported before. This phenomenon is first discovered in the synthesis of alloy nanoclusters. In addition, Pt1Ag28 nanocluster has high yield and exhibits potential optics in the near infrared (NIR) fluorescent imaging. The time-dependent density functional theory (TD-DFT) calculation implied that the optical property of Pt1Ag28 was sensitive to its structure. This work provides a simple method to synthesize alloy nanoclusters with structural isomerization.

Highly Efficient Synthesis of Au 130 (SPh-Br) 50 Nanocluster

We reported the synthesis of Au130(SPh-Br)50(Br-Ph-SH=4-bromothiophenol) nanocluster with high purity and high yield via “size focusing” and “ligand exchange” processes. The time of synthetic process was significantly reduced compared with previous synthetic routine. Au130(SPh-Br)50 was determined by UV-Vis absorption spectros-copy and matrix-assisted laser desorption ionization(MALDI) mass spectroscopy. Thermo-gravimetric analysis (TGA) and size-exclusion chromatogram(SEC) analyses confirmed the purity of Au130(SPh-Br)50. The yield of gold nanoc-lusters was 20%(based on HAuCl4).