Characterization of the active site structure of Pd and Pd-promoted Mo sulfide catalysts by means of XAFS

Recently, noble metal catalysts are noted as promising candidates for new s uper-deep-hydrodesulfurization (HDS) catalysts. In this study, we investiga ted the structure of Pd particles supported on zeolite and Al2O3 under a su lfidation or reduction condition. From EXAFS analysis, it was found for sul fided Pd catalysts that small Pd sulfide clusters are formed without sinter ing. It was also revealed that no extensive growth of metal Pd particles oc curs in Pd/NaY sulfide catalysts even after a treatment with H-2 at 673 K. The dispersion of Pd metal particles is improved by H-2/H2S treatment. Thes e results indicate that in the presence of H2S, Pd shows high resistance ag ainst particle growth. A comparison of the Mo and Pd K-edge EXAFS spectra for MoSx/Pd-NaY and Pd-N aY catalysts revealed the existence of Mo-Pd bondings by the addition of Mo sulfide, indicating a direct interaction between Mo and Pd sulfides.