Formation of carbon supported PtRu alloys: an XRD analysis

Carbon supported PtRu alloys were prepared by impregnation of Pt and Ru precursors on a porous carbon support, followed by reduction of the metals with Na2S2O4. After reduction, the samples were thermal treated in argon up to 700°C. The samples were characterized by atomic absorption (AAS) and X-ray diffraction (XRD) measurements. Before thermal treatment only carbon reflexions were visible in XRD pattern. The reflexions of face centered cubic (f.c.c.) PtRu alloy were revealed in XRD pattern starting from thermal treatment at 300°C. No hexagonal close packed (h.c.p.) RuPt reflexions were detected. During thermal treatment, part of Ru reacted with sulphur forming RuS2. Ru content in the alloy increased with increasing thermal treatment temperature. The results indicated that, first, f.c.c. Pt with few Ru alloyed was formed, then, with increasing thermal treatment temperature, part of Ru atoms present in the sample in an amorphous form entered in the crystal structure of the platinum by a diffusion-controlled mechanism. Also after thermal treatment at high temperatures there was a large part of unalloyed Ru, with only about 49% of the Ru alloyed with the Pt. PtRu particle size was in the range 15–20 nm.