XRD and raman identification of the zirconia modifications in copper/zirconia and palladium/zirconia catalysts prepared from amorphous precursors

Abstract

Recently, highly active CO{sub 2} hydrogenation catalysts have been obtained from glassy metal alloy precursors, i.e., Cu{sub 70}Zr{sub 30} and Pd{sub 33}Zr{sub 67}. During in situ activation under CO{sub 2} hydrogenation conditions, the zirconium component of the alloy is oxidized. For Pd/zirconia, the support matrix is identified as stable, monoclinic ZrO{sub 2}. In copper/zirconia, on the other hand, a metastable zirconia modification is prevalent, corresponding to either tetragonal or cubic ZrO{sub 2}. As the XRD patterns of these metastable phases are quite similar, additional information is required to distinguish between the two modifications. Both infrared and Raman spectroscopy have been established as suitable techniques to differentiate between tetragonal and cubic zirconia, as the information from the vibrational spectra is complementary to the X-ray diffraction data. In addition to the identification of the zirconia modification, particular attention is drawn in the present report to the influence of copper in amorphous Cu/Zr-alloys on the crystallization behavior of the zirconia. For comparison, two copper/zirconia catalysts were prepared by co-precipitation, drying, and subsequent reduction in a hydrogen atmosphere. These catalysts, denoted as Cu 70 and Cu 50, contain 70 at.% copper and 50 at.% copper on zirconia, respectively. In addition, the catalyst Cu 50more » was calcined at 970 K for 2 h and then rapidly quenched to room temperature. The zirconia reference samples were precipitated, dried, and calcined, or else investigated without calcination.« less