Infrared spectra of dinitrogen adsorbed on bimetallic lanthanide (Eu or Yb)–Ni/SiO₂ catalysts

Abstract

Bimetallic lanthanide (Ln: Eu or Yb)–Ni/SiO₂ catalysts prepared by the use of dissolution of lanthanide metals in liquid ammonia have been studied by infrared spectroscopy for dinitrogen adsorption. The infrared spectra were measured at 133–300 K using Ln–Ni/SiO₂ obtained when the Eu or Yb metal dissolved in liquid ammonia reacted with 20 mass% Ni/SiO₂ in different ratios. Infrared spectra for Eu–Ni/SiO₂ showed absorption bands at 2336, 2265, 2254 and 2227 cm⁻¹ at 133 K, which disappeared upon evacuation. The adsorbed state was found to be all molecular from the isotope shift using ²⁸N₂ and z³⁰N₂₈. The bands at 2254 and 2227 cm⁻¹ of them were assigned to new adsorbed dinitrogen species resulting from synergetic interactions between the europium and nickel metal. The concentration of adsorbed dinitrogen on Eu–Ni/² varied markedly with the Eu/Ni ratios, and particularly, it increased in the region of high Eu content. Upon introduction of ytterbium onto nickel, new bands at 2254 and 2226 cm^−- similarly appeared. However, the dependence of dinitrogen adsorption as a function of Yb content in Yb–Ni/SiO²> was somewhat different from that for Eu–Ni/SiO₂. The effects of lanthanide on the surface of Ln–Ni/SiO₂ were discussed in connection with the variation in catalytic properties.