Mechanically induced fcc phase formation in nanocrystalline hafnium

A face-centered-cubic (fcc) phase was obtained in high-purity hafnium (Hf) metal powders subjected to mechanical milling in a high-energy SPEX shaker mill. X-ray diffraction and electron microscopy techniques were employed to evaluate the structural changes in the milled powder as a function of milling time. The effects of mechanical milling included a reduction in grain size, an increase in lattice strain, and formation of an fcc phase instead of an equilibrium hexagonal-close-packed (hcp) phase. During milling, the grain size of Hf decreased to below about 7 nm. Additionally, there was approximately 6% increase in atomic volume during the formation of the fcc phase. Chemical analysis of the milled powder indicated the presence of significant amounts of interstitial impurities. Even though any or all of the above factors could contribute to the formation of the fcc phase in the milled powder, it appears that the high level of interstitial impurities is at least partially responsible for the formation of the fcc phase

Designing versatile nanocatalysts based on PdNPs decorated on metal oxides for selective hydrogenolysis of biomass derived γ-valerolactone and reduction of nitro aromatics

Abstract In this work, we designed versatile heterogeneous nanocatalysts based on palladium nanoparticles (PdNPs) decorated on metal oxides supports (i.e., PdNPs/γ-Al₂O₃, PdNPs/WO₃ and PdNPs/Nb₂O₅) by step-wise controlled synthesis of novel monodispersed ∼2 nm PdNPs at room temperature and then impregnated over metal oxides. PdNPs supported catalysts were characterised by powder XRD, TEM, HRTEM, NH₃-TPD, N₂-BET, H₂-TPR, and XPS techniques. PdNPs based catalysts studied in two different model reactions were presented i.e., biomass platform chemical intermediate γ-valerolactone (GVL) conversion into pentanoic acid (PA) studied in vapor phase hydrogenolysis and 4-Nitrophenol (4-NP) reduction to 4-Aminophenol (4-AP) in liquid phase using NaBH₄ as reducing agent over 0.5 wt% Pd nanoparticles -based nanocatalysts. The relationship between the active sites and the catalytic performance was evaluated. The Under optimized reaction conditions, over 0.5 wt% PdNPs/γ-Al₂O₃ catalyst exhibited the highest PA yield of 100%, and over 0.5 wt% PdNPs/WO₃, 0.5 wt% PdNPs/Nb₂O₅ exhibited PA yields of 98% and 96% respectively. Over PdNPs/γ-Al₂O₃, PdNPs/WO₃, and PdNPs/Nb₂O₅, the reduction reaction rates in the 4-NP to 4-AP are 5.40 × 10⁻³ s⁻¹, 2.55 × 10⁻³ s⁻¹ and 2.30 × 10⁻³ s⁻¹ respectively. The calculated thermodynamic parameters of the Ea values for 4-NP to 4-AP reaction were 25.30, 26.75, and 27.81 KJ/mol for the PdNPs/γ-Al₂O₃, PdNPs/WO₃ and PdNPs/Nb₂O₅, respectively