Skeletal Ni Catalysts Prepared from Amorphous Ni-Zr Alloys: Enhanced Catalytic Performance for Hydrogen Generation from Ammonia Borane.

Skeletal Ni catalysts were prepared from Ni-Zr alloys, which possess different chemical composition and atomic arrangements, by a combination of thermal treatment and treatment with aqueous HF. Hydrogen generation from ammonia borane over the skeletal Ni catalysts proceeded efficiently, whereas the amorphous Ni-Zr alloy was inactive. Skeletal Ni prepared from amorphous Ni30 Zr70 alloy had a higher catalytic activity than that prepared from amorphous Ni40 Zr60 and Ni50 Zr50 alloys. The atomic arrangement of the Ni-Zr alloy also strongly affected the surface structure and catalytic activities. Thermal treatment of the amorphous Ni-Zr alloys at a temperature slightly lower than the crystallization temperature led to an increase of the number of surface-exposed Ni atoms and an enhancement of the catalytic activities for hydrogen generation from ammonia borane. The skeletal Ni catalysts also showed excellent durability and recyclability.

Active skeletal Ni catalysts prepared from an amorphous Ni-Zr alloy in the pre-crystallization state.

Skeletal Ni catalysts were prepared from an amorphous Ni40Zr60 alloy (a-NiZr) by heating at various temperatures under vacuum, followed by the selective extraction of Zr moieties by an HF treatment. Each sample was characterized by various spectroscopic methods, and the catalytic performance was tested in the hydrogenation of 1-octene. The differences in preparation temperatures of a-NiZr strongly affected the catalytic performance of the obtained catalysts, whereby those prepared from heated a-NiZr in the pre-crystallization state exhibited higher catalytic activity. Especially, moderate thermal treatment of a-NiZr at a temperature slightly lower than that for its crystallization, that is, ~573 K, resulted in a significant enhancement of the catalytic activity. Such prepared skeletal Ni catalyst can also be used efficiently for hydrogen generation from aqueous hydrazine.

Waste-slag hydrocalumite and derivatives as heterogeneous base catalysts.

Blast furnace slag (BFS), a high-volume byproduct resulting from iron-making processes, can be considered as a low-cost and abundant precursor for preparing layered double hydroxide (LDH) compounds. Here we demonstrate that a Ca-based LDH compound (hydrocalumite) synthesized from waste BFS through facile two-step procedures and its derivatives work as useful heterogeneous base catalysts for multiple chemical reactions including the Knoevenagel condensation, oxidation of alkylaromatics with O(2), transesterification, and cycloaddition reaction of epoxides with atmospheric CO(2). Structures were verified by using XRD and thermogravimetric analysis. The surface basicity and coordination geometry of the active metal species that substantially affect the catalytic activity were investigated by CO(2)-temperature programmed desorption (TPD) and X-ray absorption fine structure (XAFS) measurements, respectively. These characterization results revealed that the slag-derived impurity elements, such as Fe, Ti, and Mn, effectively act either as active sites or as catalyst promoters in particular reactions and that the kind of guest counter anion (Cl(-) or NO(3)(-)) also plays a key role for achieving high catalytic efficiencies. In any reaction, the catalyst was easily separated by filtration and recyclable in multiple catalytic runs with retention of its activity and fine selectivity, irrespective of its considerable impurity level. It is believed that the slag-made hydrocalumite can replace existing LDH catalysts as a low-cost alternative and potentially contribute to sustainable chemical processes.

Synthesis of highly dispersed platinum nanoparticles on Ti-containing mesoporous silica using photo-assisted deposition.

A simple and unique route to synthesize the nano-size Pt particles using mesoporous silica support including single-site Ti-oxide moiety (Ti-HMS) under UV-light irradiation has been developed. By the photo-assisted deposition (PAD) method, a Pt precursor can be deposited from aqueous solution of H2PtCl6 directly on the photo-excited isolated Ti-oxide moiety. The subsequent reduction with H2 generates the nano-sized Pt metal particles (PAD-Pt/Ti-HMS). The deposition of Pt precursor onto the Ti-HMS can be recognized by the observation of the decrease in the intensity of the preedge in the Ti K-edge XANES spectrum, demonstrating that the Pt precursor underwent anchoring on the single framework Ti4+ center of Ti-HMS under UV-light irradiation. The lower intensity of the Pt-Pt bond of the PAD-Pt/Ti-HMS than that of Pt foil in the Fourier transforms of Pt L(III)-edge EXAFS spectra clearly suggests the formation of the Pt nanoparticles. The PAD-Pt/Ti-HMS exhibited the higher catalytic activity for the hydrogenation of nitrobenzene to aniline and the NO reduction than the catalyst prepared by the conventional impregnation.