HYDROGENATION CATALYSTS BASED ON NICKEL AND RARE-EARTHS OXIDES .1. RELATION BETWEEN CATIONS NATURE, PREPARATION ROUTE, HYDROGEN CONTENT AND CATALYTIC ACTIVITY

Several methods of preparation are reported for compounds based on transition metals (Me = Ni,Cu,Co) and rare earth elements (Re = La,Ce,Pr,Nd...). The starting materials were intermetallics or nitrate mixtures. In the latter case the precursors of the oxides were obtained by evaporation or coprecipitation with triethylamine or were mechanical mixtures. A ceria-supported nickel catalyst was also prepared for comparison with the first series. Whatever the preparation method, the calcined solids mainly consisted of NiO and La2O3 and/or CeO2; in the reduced state all the catalysts were hydrogen reservoirs. From a comparison taking into account specific areas, hydrogen content and catalytic activities in the hydrogenation of unsaturated hydrocarbons, it appears that the coprecipitation route produced compounds with the highest catalytic performances. When cations were varied the most active combination was Ni-Ce and in a series of Ni-Ce-O catalysts produced by coprecipitation the behaviour was found to be dependent on the Ni/Ce atomic ratio. These results lead us to propose the existence of two types of active sites.