The formation of nickel-copper alloys in zeolite Y as studied by the ferromagnetic resonance method

Samples of zeolite Y with part of their Na+ ions exchanged by Ni2+ and Cu2+ ions were dried and reduced by H2. The resulting samples were investigated by the ferromagnetic resonance method, and by measuring their catalytic properties in n-hexane conversion. The results led to the conclusion that during reduction performed above 690 K part of the Ni2+ and Cu2+ ions form largesized metal particles at the outer surface of the zeolite crystals and that these are responsible for the magnetic behavior and the catalytic activity. In almost all bimetallic samples two types of metal particles are formed, namely, ferromagnetic particles with a high Ni content and paramagnetic particles with a high Cu content. The bulk composition of the ferromagnetic alloy particles was found to be nearly constant but the surface composition proved very sensitive to the reduction temperature. The formation of the NiCu alloy was found to influence the catalytic properties for n-hexane conversion. Compared with NiY, NiCuY was less active but more selective for the isomerization because of suppressing the hydrogenolysis reaction.