Ferromagnetic resonance study of dispersed nickel particles prepared by reduction of Ni2+-exchanged X zeolites by hydrogen molecules or hydrogen atom beams

Abstract

Hydrogen atom beams have been used to prepare nickel particles at very low temperatures by reduction of nickel ions exchanged in X-type zeolite. The metal particles formed are characterised using ferromagnetic resonance (f.m.r.) and compared with those obtained by conventional thermal reduction using molecular hydrogen. Studies of the f.m.r. line-shape show that lorentzian and symmetrical lines recorded above 473 K are associated with small, homodispersed metal particles, while heterodispersion results in broadening of the symmetrical lines. Particles highly homodispersed in the zeolite supercages can be obtained if, prior to reduction at 273 K by hydrogen atom beams, a migration of Ni²⁺ ions is induced by treatment at 373 K in carbon monoxide. In the case of Ni₁₀CaX zeolite, the degree of reduction is 100 % and nickel particles of diameter 10 Å are obtained.