AN EXAFS STUDY OF SULFIDE CATALYSTS ON SILICA AS SUPPORT

The structure of the active phase of sulfide catalysts on silica as su pport were studied by means of EXAFS. Al measurements were carried und er normal conditions, on Nb-K, Re-L3, W-L3, Ni-K, and Cu-K edges. Due to the high signal-to-noise ratio of the experimental data detailed in formation about structural parameters of the active phase could be obt ained. Comparison with MoS2 data shows that both binary WS2/SiO2, ReS2 /SiO2 and NbS2/SiO2 and ternary Cu-WS2/SiO2, Ni-ReS2/SiO2 and Ni-NbS2/ SiO2 are structurally analog to MoS2. In contrast to some literature d ata a good correlation between the short Ni-S distance in DEDTC as ref erence sample and the short Ni-S distance in Cu-WS2/SiO2, Ni-ReS2/SiO2 establishes that Ni(Cu)-atoms are located in a plane square agreement with S-atoms with adding a fifth atom in a free place. Thus Ni(Cu) at oms are placed inside the plane; it seems that the Ni-NbS2/SiO2 situat ion is similar. The characteristic features of Re-L3 of Ni-ReS2/SiO2 a nd W-L3 of Cu-WS2/SiO2 spectra prove this suggestion.