X-RAY DIFFRACTION STUDIES OF Pd - Cu POWDERS. J.Pielaszek, Z.Kaszkur, B.Mierzwa - Institute of Physical Chemistry, Polish Academy of Sciences, Warszawa, Poland.

Structural changes induced by various temperature and controlled atmosphere treatments in mixtures of Pd - Cu powders were studied by in situ XRD in the aim to understand behaviour of supported Pd - Cu catalysts subjected to different pre-treatments. The position sensitive detector (PSD) CPS 120 from INEL has been used to obtain temperature scans in 10 min. intervals. The samples were carefully mixed in different weight proportion of Pd and Cu blacks of average particle sizes of 200 and 300 Å respectively. Then they were loosely spread on porous glass sample holder and placed in a controlled atmosphere XRD camera mounted on the axis of the PSD. XRD patterns were recorded for two different treatments: 1) oxidation at temperatures up to 550⁰ C followed by reduction in hydrogen up to 550⁰ C for various periods of time and 2)reduction in hydrogen up to 550⁰ C with and without transformation of palladium into its hydride at low temperatures.

Under the first treatment it was observed that different mixed oxides were formed which subsequently were reduced and, depending on the relative composition, either intermetallic solid solutions were formed (for low copper content)or complex intermetallic Pd-Cu phases (for high copper contents).

The final results obtained for the second treatment were qualitatively similar. The transformation of palladium into hydride at the first stage of hydrogen reduction had no noticeable influence on the phases formed.

The same conditions were applied for treatment of some Pd - Cu /SiO2 model catalysts with total metal loading of 2 and 10 wt.%.

The results are being rationalized in terms of the interdiffusion between initially monometallic grains and formation of different concentration profiles and intermetallic compounds within the clusters.