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. Analysis of the diffraction patterns, as a function of thermal treatment, reveals anomalous features in the evolution of Pd particles. An intermediate Pd1-xCx phase (x similar to 0.1 ) is observed and dissolved into pure Pd at similar to 700 K. Moreover, the size of metal particles, remaining almost constant (similar to 10 nm) during the annealing, abruptly increases to 30 mri in close connection with the dissolution of the Pd1-xCx phase. These effects 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-particle 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 growth in particle size, a small increase to 32 nm was observed.