Pd–Al interaction at elevated temperatures: a TEM and SAED study

Abstract

Epitaxially grown Pd particles partly embedded in amorphous Al2O3 were subjected to annealing and reductive treatments in the temperature range 523–873 K to induce a possible Pd–Al interaction. The structural, morphological and compositional changes were monitored by transmission electron microscopy and selected area electron diffraction. Formation of Pd4Al3 and PdAl alloys has been observed upon annealing in 1 bar He for 1 h at T > 523 K and upon reduction in 1 bar H2 for 1 h at T ≥ 523 K, respectively. Both alloys appear to be stable up to 873 K, although Pd4Al3 shows beginning decomposition at and above 873 K. The stability under oxidative conditions was found to be very similar, a transformation back into metallic Pd sets in for both compounds at around 573–623 K. In agreement with previous studies on Pd/SiO2, the formation of an amorphous hydride phase and/or a heavily distorted Pd lattice has been detected after reduction in hydrogen at 523 K.