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Title: Properties of pure and sulfided NiMoO{sub 4} and CoMoO{sub 4} catalysts: TPR, XANES and time-resolved XRD studies

X-ray absorption near-edge spectroscopy (XANES) was used to characterize the structural and electronic properties of a series of cobalt- and nickel-molybdate catalysts (AMoO{sub 4}.nH{sub 2}O, {alpha}-AMoO{sub 4}, {beta}-AMoO{sub 4}; A=Co or Ni). The results of XANES indicate that the Co and Ni atoms are in octahedral sites in all these compounds, while the coordination of Mo varies from octahedral in the {alpha}-phases to tetrahedral in the {beta}-phases and hydrate. Time-resolved x-ray diffraction shows a direct transformation of the hydrates into the {beta}-AMoO{sub 4} compounds (following a kinetics of first order) at temperatures between 200 and 350{degrees}C. This is facilitated by the similarities that the AMoO{sub 4}.nH{sub 2}O and H{sub 2} at temperatures between 400 and 600{degrees}C, forming gaseous water oxides in which the oxidation state of Co and Ni remains +2 while that of Mo is reduced to +5 or +4. After exposing {alpha}-NiMoO{sub 4} and {beta}-NiMoO{sub 4} to H{sub 2}S, both metals get sulfided and a NiMoS{sub x} phase is formed. For the {beta} phase of NiMoO{sub 4} the sulfidation of Mo is more extensive than for the {alpha} phase, making the former a better precursor for catalysts of hydrodesulfurization reactions.
Authors:
; ;  [1] ; ;  [2]
  1. Brookhaven National Lab., Upton, NY (United States)
  2. Centro de Quimica, Caracas (Venezuela)
Publication Date:
OSTI Identifier:
555287
Report Number(s):
BNL--64970
ON: DE98001656; TRN: 98:000152
DOE Contract Number:
AC02-76CH00016
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: [1998]
Research Org:
Brookhaven National Lab., Upton, NY (United States)
Sponsoring Org:
USDOE Office of Energy Research, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 66 PHYSICS; NICKEL OXIDES; MOLYBDENUM OXIDES; SULFIDATION; COBALT OXIDES; X-RAY DIFFRACTION; ABSORPTION SPECTRA; CATALYSTS; OXIDATION; PHASE STUDIES