Catalytic properties of lanthanide (Eu and Yb)-dosed oxides

Abstract

The lanthanide (rare earth) compounds are of considerable interest and potential from the point of view of heterogeneous catalysis. However, very little study has been carried out with a view to elucidating the origin of their unique properties. It has been shown that the catalyst systems which consist of low valent, highly dispersed lanthanide particles prepared by metal vaporization techniques exhibit specific activity [ 11. Recently, by the use of the solubility of Eu and Yb metals in liquid ammonia, we reported that active lanthanide-containing bimetallic catalysts were prepared and their catalytic properties varied markedly with the changes in lanthanlde content [2]. The present investigation is extended to include lanthanides (Eu and Yb) dispersed $311 various oxides, obtained by the reaction of the oxide powders with the solution of dissolved lanthanide metals in liquid ammonia. Their interesting catalytic properties are investigated, notably the effects of Eu or Yb surface deposition on the hydrogenation of ethylene over different oxides @Ago, SiOa, MnO and Fe304). Eu and Yb (purity: 99.9%) were obtained from the Shin-Etsu Chemical Co. MgO, referred to as JRC-MGO-3 (Reference Catalyst of the Catalysis Society of Japan [3]), was used. SiOz was the commercially available Degussa Aerosil. MnO and FeaOl were conventionally prepared by an incipient wetness technique. Manganese(B) nitrate and ferrous(N) sulfate were decomposed in basic solutions to form their hydroxide precipitates. The resulting precipitates were filtered off, washed with distilled water, dried and Anally heating under hydrogen (MnO: 673 K, 10 h and Fe304: 623 K, 7 h). The formation of the desired structures of the oxide was conflrmed by X-ray diffraction analyses (XRD). The surface areas of these oxides, determined by the BET method, were as follows: MgO= 32, SiOa= 170, MnO= 59 and Fe304=230 m2 g-l. In a typical preparation of lanthanide-dosed oxides, the oxide powders (0.84 g) which had previously been evacuated at elevated temperatures were