Ai Nozaki

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.

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.

Skeletal Au prepared from Au–Zr amorphous alloys with controlled atomic compositions and arrangement for active oxidation of benzyl alcohol

Skeletal (nanoporous) gold catalysts were prepared from Au–Zr amorphous alloys by immersion in HF solution to extract Zr moieties. The catalytic performance of the skeletal Au catalyst for the oxidation of benzyl alcohol to benzaldehyde was examined using O2 as an oxidant. The amount of benzaldehyde formed over skeletal Au treated with HF solution for 1 h was the highest among the prepared samples, despite the low surface area. Detailed characterization indicated that residual ZrO2 species on the skeletal Au promoted the oxidation reaction. The oxygen storage capacity (OSC) of skeletal Au was measured for the quantitative estimation of active sites and showed a positive correlation with the catalytic activity of skeletal Au, verifying the presence of Au–ZrO2 interfaces. Skeletal Au was also prepared from a Au–Zr crystalline alloy and its catalytic activity was compared with that of the one prepared from the amorphous alloy. The atomic arrangement of the Au–Zr amorphous alloy had a strong effect on the catalytic activity due to the surface structure (coordination number and morphology) of skeletal Au. The unsaturated Au atoms created in the skeletal Au catalysts contributed to the reduction of activation energy for oxidation of benzyl alcohol.