Guozhu Chen

Synthesis of Ni–Ru Alloy Nanoparticles and Their High Catalytic Activity in Dehydrogenation of Ammonia Borane

We report the synthesis and characterization of new Ni(x)Ru(1-x) (x = 0.56-0.74) alloy nanoparticles (NPs) and their catalytic activity for hydrogen release in the ammonia borane hydrolysis process. The alloy NPs were obtained by wet-chemistry method using a rapid lithium triethylborohydride reduction of Ni(2+) and Ru(3+) precursors in oleylamine. The nature of each alloy sample was fully characterized by TEM, XRD, energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). We found that the as-prepared Ni-Ru alloy NPs exhibited exceptional catalytic activity for the ammonia borane hydrolysis reaction for hydrogen release. All Ni-Ru alloy NPs, and in particular the Ni(0.74)Ru(0.26) sample, outperform the activity of similar size monometallic Ni and Ru NPs, and even of Ni@Ru core-shell NPs. The hydrolysis activation energy for the Ni(0.74)Ru(0.26) alloy catalyst was measured to be approximately 37 kJ mol(-1). This value is considerably lower than the values measured for monometallic Ni (≈70 kJ mol(-1)) and Ru NPs (≈49 kJ mol(-1)), and for Ni@Ru (≈44 kJ mol(-1)), and is also lower than the values of most noble-metal-containing bimetallic NPs reported in the literature. Thus, a remarkable improvement of catalytic activity of Ru in the dehydrogenation of ammonia borane was obtained by alloying Ru with a Ni, which is a relatively cheap metal.

Bifunctional catalytic/magnetic Ni@Ru core–shell nanoparticles

Core-shell structured Ni@Ru bimetallic nanoparticles are demonstrated as a bifunctional nanoplatform system for the hydrolysis reaction of ammonia-borane and also for magnetic separation.

Facile and Mild Strategy to Construct Mesoporous CeO2–CuO Nanorods with Enhanced Catalytic Activity toward CO Oxidation

CeO2-CuO nanorods with mesoporous structure were synthesized by a facile and mild strategy, which involves an interfacial reaction between Ce2(SO4)3 precursor and NaOH ethanol solution at room temperature to obtain mesoporous CeO2 nanorods, followed by a solvothermal treatment of as-prepared CeO2 and Cu(CH3COO)2. Upon solvothermal treatment, CuO species is highly dispersed onto the CeO2 nanorod surface to form CeO2-CuO composites, which still maintain the mesoporous feature. A preliminary CO catalytic oxidation study demonstrated that the CeO2-CuO samples exhibited strikingly high catalytic activity, and a high CO conversion rate was observed without obvious loss in activity even after thermal treatment at a high temperature of 500 °C. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and hydrogen temperature-programmed reduction (H2-TPR) analysis revealed that there is a strong interaction between CeO2 and CuO. Moreover, it was found that the introduction of CuO species into CeO2 generates oxygen vacancies, which is highly likely to be responsible for high catalytic activity toward CO oxidation of the mesoporous CeO2-CuO nanorods.

Semiconductor and Metallic Core–Shell Nanostructures: Synthesis and Applications in Solar Cells and Catalysis

Nano-heterostructures have attracted great attention due to their extraordinary properties beyond those of their single-component counterparts. This review focuses on a specific type of hybrid structures: core-shell structures. In particular, we present and discuss the recent wet-chemical synthesis approaches for semiconductor and metallic core-shell nanostructures, and their relevant properties and potential applications in photovoltaics and catalysis, respectively.

Shape-controlled synthesis of ruthenium nanocrystals and their catalytic applications

The catalytic properties of ruthenium (Ru) are fairly well known. Nevertheless its shape-controlled synthesis (especially as compared to other noble metals) is still elusive. In this review, we present recent advances in the synthesis of Ru nanomaterials, in particular, spherical nanoparticles, one dimensional nanostructures, nanoplates and hollow structures, as well as other examples. In addition, the catalytic applications of Ru materials are selectively surveyed. Finally, the challenges and perspectives on the controlled synthesis of Ru-based nanomaterials and their catalytic applications are described.

Interfacial reaction-directed synthesis of a ceria nanotube-embedded ultra-small Pt nanoparticle catalyst with high catalytic activity and thermal stability

A catalyst based on ceria nanotube-embedded ultra-small Pt nanoparticles was synthesized by means of an interfacial reaction in the absence of any surfactant and without involving any separate surface modification process. When Ce(OH)CO3 nanorods and H2PtCl6 are introduced into a NaOH aqueous solution in sequence, a solid–liquid interfacial reaction between Ce(OH)CO3 and NaOH occurs. The formed Ce(OH)3 then deposits on the external surface of Ce(OH)CO3 nanorods. During the interfacial reaction, the negatively charged Pt species is expected to be electrostatically attracted to gradually formed Ce(OH)3 due to its positive charge, resulting in a uniform mixture of Pt species and Ce(OH)3. After removing residual Ce(OH)CO3 and hydrogen reduction, ceria nanotube-embedded Pt nanoparticle hollow composites were achieved. Due to the ultra-small size of catalytically active Pt nanoparticles and the close contact between Pt and ceria, the catalyst exhibits high catalytic activity toward CO oxidation and excellent thermal stability even at temperatures as high as 700 °C, suggesting that they also hold promise for higher temperature catalytic reactions.

Solubility product difference-guided synthesis of Co3O4–CeO2 core–shell catalysts for CO oxidation

It is still an important issue to develop a facile, environmentally friendly way to synthesize bimetal oxide materials. In this paper, Co3O4–CeO2 core–shell catalysts were prepared by an interfacial reaction, where Co(CO3)0.35Cl0.2(OH)1.1 nanorods were dispersed in Ce3+ aqueous solution for 2 days, followed by a calcination step. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Based on the characterization and comparative experimental results, we proposed that the OH− ions slowly dissociated from the Co(CO3)0.35Cl0.2(OH)1.1 precursor combined with Ce3+ to develop into Ce(OH)3 nanoparticles because of its smaller solubility product constant than that of the Co precursor or Co(OH)2. Neither an additional precipitation agent nor stabilizing molecules were employed during the whole preparation. Raman spectroscopy and H2-temperature programmed reduction (H2-TPR) analysis revealed that there is a synergistic effect between Co3O4 and CeO2 in the as-prepared Co3O4–CeO2 core–shell catalysts, which is responsible for their enhanced catalytic activity toward CO oxidation in comparison to pure Co3O4 and CeO2.

Design of Porous/Hollow Structured Ceria by Partial Thermal Decomposition of Ce-MOF and Selective Etching

Metal-organic frameworks (MOFs) have been widely used to prepare corresponding porous metal oxides via thermal treatment. However, high temperature treatment always leads to obtained metal oxides with a large crystallite size, thus decreasing their specific surface area. Different from the conventional complete thermal decomposition of MOFs, herein, using Ce-MOF as a demonstration, we choose partial thermal decomposition of MOF, followed by selective etching to prepare porous/hollow structured ceria because of the poor stability of Ce-MOF under acidic conditions. Compared with the ceria derived from complete thermal decomposition of Ce-MOF, the as-prepared ceria is demonstrated to be a good support for copper oxide species during the CO oxidation catalytic reaction. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and hydrogen temperature-programmed reduction (H2-TPR) analysis revealed that the as-prepared ceria is favorable for strengthening the interaction between the ceria and loaded copper oxide species. This work is expected to open a new, simple avenue for the synthesis of metal oxides from MOFs via partial thermal decomposition.

Room temperature interfacial reaction-directed synthesis of hierarchically porous ceria from a water-soluble precursor

Unlike the conventional calcination of cerium precursors at elevated temperature, hierarchically porous ceria was successfully synthesized via an interfacial reaction between the water-soluble cerium sulfate (Ce2(SO4)3) precursor and NaOH in ethanol at room temperature. Neither additional surfactant molecules nor calcination was employed during the whole preparation process. It was found that the as-prepared ceria inherited well the shape and dimensions of the hierarchically flowerlike Ce2(SO4)3 precursor after the interfacial reaction. The concentration of sulfuric acid was demonstrated to play a great role in controlling the precursors morphology. Compared with ceria derived from direct calcination of the same Ce2(SO4)3 precursor, the one obtained from the interfacial reaction was far more reactive in CO oxidation due to its well-retained hierarchically porous morphology and high surface area. This work is expected to open a new, simple avenue for the synthesis of hollow nanomaterials from water-soluble precursors.

One-pot synthesis of Pt−Cu bimetallic nanocrystals with different structures and their enhanced electrocatalytic properties

Shape-controlled synthesis of Pt−Cu alloy nanocrystals (NCs) with unique geometries is of great importance in the rational design and deterministic synthesis of highly active electrocatalysts. Herein, Pt−Cu alloy NCs with concave octahedron (COH), porous octahedron (POH), yolk–shell (YSH), and nanoflower (NOF) structures were fabricated by altering the sequential reduction kinetics in a one-pot aqueous phase. The effect of the reaction kinetics on the formation of Pt−Cu bimetallic NCs with different morphologies was analyzed quantitatively. The concentrations of glycine and metal cation are demonstrated to play a key role in the reduction of Pt(IV) and Cu(II) ions; these significantly affected the morphology of Pt−Cu NCs. These Pt−Cu alloy NCs exhibit substantially enhanced catalytic activity and durability for methanol and formic acid oxidation compared to the commercial Pt/C catalyst. Specifically, the COH and NOF Pt−Cu NCs with more step atoms, intragranular dislocations, and protrusions showed superior electrochemical properties than those of POH and YSH Pt−Cu NCs. The structure–property relationship between the Pt−Cu NCs and their electrochemical performances was also investigated in depth.