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Metallic nickel is known to efficiently catalyze hydrogenation reactions, but one of its major drawbacks lies in its lack of selectivity, linked to side-reactions of hydrogenolysis and over-hydrogenation. More selective hydrogenations can be obtained upon the introduction of a second metal in combination with Ni. Fe is an interesting choice, as it is a cheap and abundant metal. This review aims at discussing the advantages and constraints brought by the preparation procedures of bimetallic supported Ni–Fe nanoparticles, and at analyzing the benefits one can draw by substituting Ni–Fe supported catalysts for Ni monometallic systems for the catalytic hydrogenation of organic molecules. Specific formulations, such as Ni75Fe25, will be singled out for their high activity or selectivity, and the various hypotheses behind the roles played by Fe will be summarized.

Direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol has recently drawn much attention because such a process would allow the application of the green chemistry principles. However, its...

A monometallic Ni and a bimetallic Ni-Fe catalyst were used in the aqueous phase hydrogenation of xylose in batch conditions (T = 50 -150 °C, PH2 = 10 -30 bar, xylose mass fraction in water = 3.7 -11.0 wt.%) to evidence the benefits of promoting Ni by Fe. The activity of the catalysts increased with temperature, but a temperature of 80 °C allowed minimizing nickel leaching at full conversion. The presence of reduced Fe at the surface of the bimetallic nanoparticles increased both the first-order apparent rate constant and the adsorption constant of xylose. The catalytic activity of Ni/SiO2 strongly declined and no deactivation was found for the Ni-Fe catalyst. A restructuring of the bimetallic nanoparticles took place, as the size of the metal particles and the Fe proportion in the surface layers increased, suggesting a flattening and coalescing of the particles over the silica surface.

The exposure of the crystallographic facets of CeO 2 nanocrystals may alter their surface structure and composition, leading to significant discrepancies in their reactivity with respect to catalyzing different reactions. In this paper, a facile strategy of etching hollow CeO 2 spheres (@CeO 2 ) with a fluorine-containing ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]ijBF 4 ]), under hydrothermal conditions was developed to achieve surface-fluorinated @CeO 2 nanoparticles with exposed active high-energy facets, which were further assembled in situ into @CeO 2 nanoparticle assemblies. The IL, [Bmim][BF 4 ], is believed to play an important role in determining the formation of CeO 2 nanoparticles, and the mild release of fluorine species from [Bmim][BF 4 ] may account for the surface-fluorination and the exposure of active high-energy facets of CeO 2 . The CeO 2 nanoparticle assemblies are ideal model materials for studying crystal facet-dependent catalytic behavior. By loading well-dispersed Au nanoparticles via a sol-impregnation method, @CeO 2 /Au nanoparticle assemblies were achieved, which showed an enhanced catalytic performance for benzyl alcohol aerobic oxidation. In comparison with @CeO 2 /Au nanoparticle assemblies obtained by etching @CeO 2 spheres with other fluorine-containing agents, NH 4 BF 4 , NaBF 4 , and NH 4 F, under identical reaction conditions, @CeO 2 /Au nanoparticle assemblies achieved by etching with [Bmim][BF 4 ] exhibited the highest catalytic activity for benzyl alcohol aerobic oxidation. The surface-fluorination and the exposure of active high-energy facets of CeO 2 nanoparticles are believed to be responsible for the enhancement of their catalytic activity. This methodology provides a robust strategy to create CeO 2 materials with the active high-energy facets exposed and afford model materials for investigating crystal facetdependent catalytic behavior, which currently represents an exciting issue in the nanocatalysis community.

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A facile hydrothermal etching process was developed to synthesize TiO 2 /Ag nanocubes for enhanced photocatalytic application. The synthesis was carried out by chemically etching hollow @TiO 2 spheres in the presence of an AgF or AgF/NaF solution under hydrothermal conditions. Utilizing F − as a morphologydirecting agent and Ag + as an Ag source during the etching process, TiO 2 nanocubes can be easily formed with their active high-energy facets exposed and Ag nanoparticles can be in situ deposited simultaneously on the surface of the TiO 2 nanocubes to generate hybrid TiO 2 /Ag nanocubes. The resulting TiO 2 /Ag nanocubes were well controlled with Ag nanoparticles uniformly distributed on the surface of the TiO 2 nanocubes. The morphologies of TiO 2 /Ag can be altered from ellipsoidal to cubic shapes depending on the amounts of AgF or AgF/NaF used for chemical etching. Due to the exposure of the active high-energy facets of TiO 2 and the uniform deposition of Ag nanoparticles, the obtained TiO 2 /Ag nanocubes showed superior catalytic performance for the photocatalytic degradation of rhodamine B under visible-light radiation. It is proposed that the surface plasmon resonance effect arisen from Ag nanoparticles on TiO 2 nanocubes can effectively enhance the visible-light driven photocatalytic properties of TiO 2 /Ag photocatalysts. Meanwhile, due to the etching of F ions during the synthetic process, the morphology variation of TiO 2 from spherical to cubic shapes may be beneficial to the exposure of high energy {001} facets, which is liable to produce more electron-hole pairs in the photocatalytic process, and electron-hole pairs can combine with OH − to produce large amounts of hydroxyl radicals, eventually accelerating the decomposition of the organic dye.