Formation of carbon supported PtRu alloys: an XRD analysis

Carbon supported PtRu alloys were prepared by impregnation of Pt and Ru pre cursors on a porous carbon support. followed by reduction of the metals wit h Na2S2O4. After reduction, the samples were thermal treated in argon up to 700 degreesC. The samples were characterized by atomic absorption (AAS) an d X-ray diffraction (XRD) measurements. Before thermal treatment only carbo n reflexions were visible in XRD pattern. The reflexions of face centered c ubic (f.c.c.) PtRu alloy were revealed in XRD pattern starting from thermal treatment st 300 degreesC. No hexagonal close packed (h.c.p.) RuPt reflexi ons were detected. During thermal treatment, part of Ru reacted with sulphu r forming RuS2. Ru content in the alloy increased with increasing thermal t reatment 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 th e crystal structure of the platinum by a diffusion-controlled mechanism. Al so after thermal treatment at high temperatures there was a large part of u nalloyed Ru. with only about 49% of the Ru alloyed with the Pt. PtRu partic le size was in the range 15-20 nm. (C) 2001 Elsevier Science B.V. All right s reserved.