Zhixin Yu

Nanostructuring gold wires as highly durable nanocatalysts for selective reduction of nitro compounds and azides with organosilanes

A general method is developed to prepare durable hybrid nanocatalysts by nanostructuring the surface of gold wires via simple alloying and dealloying. The resulting nanoporous gold/Au (NPG/Au) wire catalysts possess nanoporous skins with their thicknesses on robust metal wires specified in a highly controllable manner. As a demonstration, the as-obtained NPG/Au was shown to be a highly active, chemo-selective, and recyclable catalyst for the reduction of nitro compounds and azides using organosilanes as reducing agents.

Size-Dependent Catalytic Activity of Monodispersed Nickel Nanoparticles for the Hydrolytic Dehydrogenation of Ammonia Borane

Nickel (Ni) nanoparticles (NPs) with controlled sizes in the range of 4.9-27.4 nm are synthesized by tuning the ratio of the nickel acetylacetonate precursor and trioctylphosphine in the presence of oleylamine. X-ray diffraction and transmission electron microscopy confirm the formation of the metallic Ni crystal phase and their monodispersed nature. These Ni NPs are found to be effective catalysts for the hydrolytic dehydrogenation of ammonia borane, and their catalytic activities are size-dependent. A volcano-type activity trend is observed with 8.9 nm Ni NPs presenting the best catalytic performance. The activation energy and turnover frequency (TOF) of the 8.9 nm NP catalyst are further calculated to be 66.6 kJ·mol-1 and 154.2 molH2·molNi-1·h-1, respectively. Characterization of the spent catalysts indicates that smaller-sized NPs face severe agglomeration, resulting in poor stability and activity. Three carbon support materials are thus used to disperse and stabilize the Ni NPs. It shows that 8.9 nm Ni NPs supported on Ketjenblack (KB) exhibit higher activity than that supported on carbon nanotubes and graphene nanoplatelets. The agglomeration-induced activity loss is further illustrated by immobilizing 4.9 nm Ni NPs onto KB, which exhibits significantly enhanced activity with a high TOF of 447.9 molH2·molNi-1·h-1 as well as an excellent reusability in the consecutive dehydrogenation of ammonia borane. The high catalytic performance can be attributed to the intrinsic activity of nanoparticulate Ni and the improved activity and stability due to the strong Ni/KB metal-support interactions.

Facile reduction of aromatic nitro compounds to aromatic amines catalysed by support-free nanoporous silver

Nanoporous silver was used as the catalyst for the reduction of aromatic nitro compounds even in the presence of some sensitive functional groups under mild conditions with excellent yields. A reduced amount of NaBH4 was used. The reaction kinetics was studied with the help of UV-visible spectrophotometry.

Bimetallic PdCo catalyst for selective direct formylation of amines by carbon monoxide

A highly efficient and selective bimetallic Pd0.88Co0.12 nanoparticle catalyst was developed for the direct N-formylation of amines by carbon monoxide. This catalyst is compatible with a wide range of substrates, affording various synthetically useful formamides under practical and mild reaction conditions.

Nickel Cobalt Thiospinel Nanoparticles as Hydrodesulfurization Catalysts: Importance of Cation Position, Structural Stability, and Sulfur Vacancy

First-row transition metal-based thiospinels are prepared via a one-pot versatile strategy and for the first time investigated as hydrodesulfurization (HDS) catalysts. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy analysis confirm that these thiospinels consist of agglomerated nanoparticles (NPs) and contain multivalent metal cations. Among the sulfides synthesized at 230 °C, NiCo2S4 presents the highest thiophene conversion. This high intrinsic activity is found to be correlated with the normal spinel structure with Ni cations located on the tetrahedral sites and Co cations on the octahedral sites. However, the spent NiCo2S4 NPs experience phase transformation because of the relatively low synthetic temperature. Accordingly, six NiCo2S4 samples are prepared in the temperature range of 180-350 °C, and their HDS activity increases monotonically with the synthetic temperature, which is attributed to the higher structural stability and more surface sulfur vacancy of the NiCo2S4 NPs prepared at higher temperatures. Notably, the NiCo2S4 NPs synthesized at 350 °C exhibit a much higher thiophene conversation of 62.9% than the classic MoS2 catalyst (39.3%) as well as excellent reusability. Our study suggests that the NiCo2S4 thiospinels with high activity and stability can represent a new promising class of industrial HDS catalysts.

Nickel Decorated Carbon Nanocomposites as Catalysts for the Upgrading of Heavy Crude Oil

Nickel (Ni) nanoparticles (NPs) supported onto different carbon nanomaterials, including ketjenblack carbon, carbon nanotubes and graphene nanoplatelets, and zeolite are prepared via the wet chemical method and employed as catalysts for the viscosity reduction of heavy crude oil. X-ray powder diffraction and transmission electron microscopy confirm the formation and uniform dispersion of Ni NPs with an average particle size of ca. 9 nm on the surface of supports. Thermogravimetric analysis is used to determine the content of Ni NPs in the nanocomposites. The specific surface area and pore volume are studied by the N2 adsorption–desorption surface area analyzer. Furthermore, catalytic aquathermolysis is conducted in a batch reactor containing HCO, hydrogen donor and the as-prepared nanocomposites under conditions of temperatures of 200-300 °C and pressures of 2-5 MPa. Parameters, such as temperature, hydrogen donor, catalyst dosage and reaction time, are further investigated to improve the catalytic activity. It is discovered that with the nanocomposite catalysts, high viscosity reduction ratio of 97% is achieved and undesirable viscosity regression is not observed. These results suggest that carbon supported Ni nanocomposites can serve as a promising candidate catalyst for the future implementation in the in-situ upgrading and recovery of HCO.