Thermal evolution of carbon-supported Pd nanoparticles studied by time-resolved X-ray diffraction

Time-resolved X-ray diffraction measurements were performed in situ on a Pd /C catalyst during two successive thermal treatments from 300 to 873 K. Ana lysis of the diffraction patterns, as a function of thermal treatment, reve als anomalous features in the evolution of Pd particles. An intermediate Pd 1-xCx phase (x similar to 0.1 ) is observed and dissolved into pure Pd at s imilar to 700 K. Moreover, the size of metal particles, remaining almost co nstant (similar to 10 nm) during the annealing, abruptly increases to 30 mr i in close connection with the dissolution of the Pd1-xCx phase. These effe cts clearly point out an interaction between the metal and the support and suggest that the formation of the Pd1-xCx phase would prevent the metal-par ticle sintering, thus maintaining the catalyst dispersion at a high level. There is no evidence of the formation of a Pd1-xCx phase during the second temperature treatment since only metallic Pd was detected. As for the growt h in particle size, a small increase to 32 nm was observed.