Preparation of some rare earth oxide supported rhodium catalysts: Study of the supports

The present work deals with the preparation of some lanthana, samaria and ytterbia supported rhodium catalysts. The three oxides used as starting supports are actually hydrated and carbonated in bulk; the intensity of the processes, and even the nature of the resulting phases are quite different from each other. It has been found that the impregnation process induces further carbonation of lanthana, to such an extent that the carbonated phase becomes the major component of the support. No similar effects could be detected on samaria and ytterbia. From the study of the reduction step, experimental conditions which allow the preparation of true rare earth oxide supported rhodium catalysts have been devised. In order to achieve this, reduction temperatures ranging from 723 K (La 2 O 3 ) to 623 K (Yb 2 O 3 ) were found to be necessary. In the case of lanthana the phases resulting from the use of lower reduction temperatures were also studied. It can be concluded from the present work that the behaviour as support of lanthanide oxides, particularly in the case of lanthana, is even more complex than had been presumed earlier.