The Structural Dynamics Behind the Formation of α’-Ni3Ga Alloy Nanoparticles from a Ni-Ga Phyllosilicate Dispersed on Silica Using X-ray Probes

This study investigates the structural evolution during the formation of α’-Ni3Ga alloy nanoparticles from Ni-Ga phyllosilicate sheets upon heating in H2. The phyllosilicate sheets were produced through a deposition-precipitation process using Ni and Ga nitrates and colloidal SiO2. Advanced characterization techniques, including X-ray absorption spectroscopy, pair distribution function analysis, and electron microscopy, revealed the structure of the chrysotile-type phyllosilicates. Such phyllosilicates are composed of brucite-like layers with Ni2+ in octahedral coordination with oxygen (NiO6), intercalated by layers of silica tetrahedra (SiO4). Ga3+ ions partially replaced Ni2+ in octahedral positions within the brucite-like layers, but are also found in tetrahedral coordination, substituting Si4+ within the SiO4 layers of the phyllosilicate phase and/or dispersed on/in the surface of the amorphous SiO2 support. The structural transformation of the precursor material during thermal activation in H2 was monitored by d-PDF and XAS. It was observed that the decomposition of the Ni-Ga phyllosilicate starts in the temperature range 100 - 200 °C, resulting in the formation of small nickel-rich nanoparticles and gallium oxide (GaOx) species. As the temperature is increased, Ga is reduced and is incorporated into the metallic nickel structure, ultimately forming intermetallic α’-Ni3Ga nanoparticles with an average size of about 5 nm. Our findings provide a detailed mechanistic understanding of the structural evolution of the phyllosilicate-based precursor, including alloy/intermetallic formation under thermal reduction conditions and highlight the potential of mixed-metal phyllosilicates as precursors for bimetallic catalysts.