Structure of the molybdenum sulfide phase in carbon-supported molybdenum and cobalt-molybdenum sulfide catalysts as studied by EXAFS

Exafs study of the local structure of Ni in Ni-MoS2/C hydrodesulfurization catalysts

“…An inverse transformation over a limited r range gave the EXAFS function of the desired single shell absorber-scatterer pair. Phase shifts and backscattering amplitudes for the Mo-S and Mo-Mo pairs were taken from the Mo K EXAFS spectrum of MoS2 [9]. (l/A) R (A) In order to remove higher shell contributions and contributions due to low and high frequency noise the Ni EXAFS spectrum of the Ni-MoS2/C catalyst was Fourier transformed over the interval k= 3.1-11.18 ~-1 (k3 weighing) and inverse Fourier transformed over the range R = 0.52-3.35 A.…”

“…The Mo-S coordination number of this promoted catalyst is higher than that of the unpromoted MoS2/C catalyst (table 2) and is in fact, within the uncertainty of the measurement, equal to that in bulk MoS 2. This shows that the Mo atoms in the promoted catalyst are fully coordinated by sulfur atoms, like in sulfided Co-Mo/C [9] and Co-Mo/A1203 [13] catalysts. This increased sulfur coordination of the Mo atoms is most probably related to the sulfur atoms which accompany the promoter atoms for stoechiometric reasons.…”

“…The exact position of the Co or Ni atoms at the edges of the MoS 2 crystallites in the Co-Mo-S structure has still to be established, although informative EXAFS and XANES results have been published by Topsoe et al [6] and by Bouwens et al [7][8][9][10]. Since the beryllium windows of the in-situ EXAFS cell used in our investigations [7][8][9][10] contained a small amount of Ni, the Co EXAFS k-range which could be measured for Co-MoS 2 catalysts was somewhat limited.…”

“…Since the beryllium windows of the in-situ EXAFS cell used in our investigations [7][8][9][10] contained a small amount of Ni, the Co EXAFS k-range which could be measured for Co-MoS 2 catalysts was somewhat limited. Therefore we decided to study the Ni K edge EXAFS spectra of Ni-MoS2/C catalysts.…”

A Mo–K Edge XAFS Study of the Metal Sulfide-Support Interaction in (Co)Mo Supported Alumina and Titania Catalysts

“…Phase shifts and backscattering amplitudes obtained from reference compounds were used to calculate the EXAFS contributions: Na 2 MoO 4 ·2H 2 O for the Mo-O, and MoS 2 for the Mo-S and Mo-Mo contribution. Details of the references are described elsewhere (15). Phase shifts and backscattering amplitudes for the Mo-Al and Mo-Ti contributions were theoretically calculated with the FEFF-3.1 program.…”