Photon Factory Activity Report 2005 #23 Part B (2006)
Chemistry

10B, 7C, 9C/2004G117

Clarification of the effects of chelate-added hydrodesulfurization catalyst bymeans of in-situ XAFS
Takeshi KUBOTA*1, Masataka ITO1, Takeshi KADONO1, Yasuaki OKAMOTO1
1
Department of Material Science, Shimane-Univ.,
Matsue, Nishikawatsu, Shimane 690-8504, Japan

Experimental
Co(Ni)-W/Al2O3 catalyst were prepared by a double
impregnation method in the presence or absence ofnitrilotriacetic acid (NTA) as a chelating compound(NTA/Co(Ni) mole ratio = 1.0). The catalysts were driedat 373 K overnight. The W and Co or Ni contents were
16.7 and 2.7 wt.% for the all catalysts.
The Co and Ni K-edge XAFS spectra for Co-Mo, Ni-W
and Co-W catalysts were measured at BL-9A or BL-7C
of KEK-IMSS-PF in a fluorescence mode under in situ
conditions [1].
Results and Discussion
It was found from Figure1 that the Co species in a CoW/Al2O3 catalyst prepared by a double impregnation
method (uncalcined after Co addition) were sulfided evenat room temperature. Sulfidation of Co rapidly prceededwith increasing temparature and almost completed at473K. On the other hand, the Co species of a Co-W/Al2O3
catalyst with nitrilotriacetic acid (NTA) were scarcely
sulfided at room temperature. Furthermore, the rate ofsulfidation was very slow compared with the catalyst
prepared without NTA addition even at a higher
temperature [2]. With each catalyst, isosbestic points
appeared in the series of XANES spectra, indicating thatthese XANES spectra consist of two components of thespectra due to oxide and sulfide species. We analyzed thespectra by assuming a linear combination of these Cospecies. The calculated spectra showed good agreementwith the measured spectra. It is obvious from Figure 2
that the sulfidation of Co is significantly depressed by theaddition of NTA. Comparison of the spectra for the both
catalyst systems indicates that the formation of Co9S8 isalso suppressed by the addition of NTA. It is clearly
demonstrated that the addition of NTA hinders sulfidationof Co, leading to a selective formation of a Co-W-S phase.

16Users' Report

NTA/Co-W/Al2O3
Normalized absorbance / a.u.

Introduction
Currently, Co-Mo sulfide catalysts are used for HDS
treatment. It is well known that catalytic synergy
generates between Co and Mo sulfides in the catalyst
system. In the industrial catalysts, chelating agents areadded to catalysts to improve HDS activity. However, therole for the catalysts properties in the addition ofchelating agents are not clarified in detail.
In this study, the chemical state analysis of Co and Ni
in Co-W and Ni-W sulfide catalysts are studied by meansof an in situ fluorescence XAFS technique.

Co-W/Al2O3in airRT373K

473K
573K
623K

77007750
Photon energy / eV
Figure 1 Co K-edge XANES spectra for Co-W/Al2O3
and NTA-Co-W/Al2O3 during the sulfidation treatment.
10080
60
40
Co-W(Co)
NTA-Co-W(Co)20

Co-W(W)
NTA-Co-W(W)
0300

400

500

600

700

800

Temperature / K
Figure 2. Degree of sufidation of Co and W obtained
by XANES analysis against the sulfidation temperature
for Co-W/Al2O3 catalysts
References[1] K.K. Bando et al., Topics in Catal., 18, 59 (2002).
[2] T. Kubota et al., J. Phys. Chem. Chem. Phys., 5, 4510
(2003).
* kubotake@riko.shimane-u.ac.jp