Phase examination of 5 mol% Nd_2O_3-doped ZrO_2 from a coprecipitation process

摘要

The oxide fine particles in the ZrO2-R2O3 (R:rare earths) system are useful components of catalytic materials such as supports and promoters in chem-ical syntheses and pollution controlling reactions [1,2], besides being raw powders for ion-conducting and tough ceramics [3]. In a previous paper [4] Nd203-doped ZrO2, in use as a large surface-area support of iron oxide catalyst, was examined for the removal of carbon monoxide at low temperatures. Enhancement of the oxidation activity was observed in the 2.5-5 mol % Nd203-doped ZrO2. These were synthesized by a coprecipitation process followed by heat treatments at low (500-800 CC) temperatures. The improved performance should be related to adsorption of oxygen or carbon monoxide molecules on the activated sites which involve oxygen defects, as is the case in Y203-doped ZrO2 for methanol synthesis [5]. Knowledge of the crystal structure of Nd2O3-doped ZrO2 is useful in understanding the surface chemistry associated with these active de-fects. However, a previous preliminary X-ray dif-fraction (XRD) observation failed to clarify the symmetry of these ZrO2 [4]. Few detailed XRD studies have been reported for the Nd2O3-ZrO2 system synthesized by a coprecipitation process because of the poor crystallinity resulting from the presence of metastable mixed phases and lattice strain. In this letter, we describe the results of a re-examination of the 5mol% Nd2O3-doped ZrO2 powder using the Rietveld fitting technique for X-ray and neutron diffraction [6-9]. These data are important to the study of catalytic effects in modified zirconia.