Photon Factory Activity Report 2004 #22 Part B (2005)
Applied Science

10B/2003G297

Effect of CyDTA on the coordination structure around Ni atom during thepreparation steps for NiMo and NiW hydrodesulfurization catalysts
Naoto Koizumi, Kentaro Hata, Yuka Murata, Masahiro Shingu and Muneyoshi Yamada*
Department of Applied Chemistry, Graduate School of Engineering, Tohoku University,
6-6-07 Aoba, Aramaki, Sendai, 980-8579 Japan
Introduction
NiMo/Al2O3 and NiW/Al2O3 catalysts are widely usedfor the hydradesulfurization (HDS) and hydrogenation(HYD) reactions of petroleum feedstock. It is an urgent
issue to improve their catalytic activity to meet severe
regulations for the sulfur content of the transportation
fuels. These catalysts are usually prepared byimpregnating Al2O3 support with an aqueous solution
containing Ni and Mo (or W). The impregnated materials
are further underwent a drying process and finallysulfided before the reaction. Recently, the authors foundthat the addition of some chelating agents such as CyDTA
to the impregnation solution greatly improves their HDS
and HYD activities [1, 2]. Thermodynamic calculations
imply that CyDTA forms a stable complex with Ni ion in
the impregnating solution, which survives during theimpregnation and drying process and eventually affects
the sulfide structures [2]. However, no direct evidence forthe role of CyDTA during the preparation steps has beenreported yet. Therefore, the present study has investigatedthe coordination structure around Ni atoms during thepreparation of NiMo and NiW catalysts by Ni K-edge
EXAFS. The local structures around Mo and/or W atoms
in these catalysts are also reported in the separate report.
Experimental
Ni K-edge EXAFS spectra for NiMo/Al2O3 andNi/W/Al2O3 catalysts after drying and impregnating steps
were measured at room temperature in a transmission
mode at BL10B and BL12C. After the background3
subtraction, k -weightened EXAFS functions wereFourier transformed into a R space and then curve-fitting
analyses were carried out in the R space. Backscattering
amplitude and phase shift for Ni-O bond inpolycrystalline NiO were used for the curve-fitting
analyses of the supported catalysts. Detailed proceduresfor the catalyst preparation were given in ref. [2].

Results and Discussion
Fourier transformed EXAFS spectrum for NiW/Al2O3
catalyst prepared without CyDTA after drying process
showed only one Ni-O shell. Because the interatomic
distance of this shell (0.205 nm, see Table) is comparablewith that of Ni-O bond in NiCl2·H2O [3], it is suggested
that Ni species in this catalyst predominantly exists asNi(II) coordinated by H2O in an octahedral environment.
On the other hand, another Ni-O shell having theinteratomic distance of 0.282 nm was observed in Fouriertransformed spectrum for NiW/Al2O3 catalyst preparedwith CyDTA after drying process. It is noted that a similar(but not the same) Fourier transformed spectrum was also
obtained with NiW/Al2O3 catalyst prepared with CyDTA
after the impregnation step (not shown here). In the caseof NiMo/Al2O3 catalyst prepared with CyDTA after thedrying process, two Ni-O shells were also observed in
Fourier transformed EXAFS spectrum. Their structuralparameters are consistent well with those observed forNiW/Al2O3 catalyst prepared with CyDTA as shown in
Table. On the contrary, only one Ni-O shell was observedin the spectrum for NiMo/Al2O3 catalyst prepared without
CyDTA after the drying process. Although the origin of
the second Ni-O shell is not clear yet at present, thepresent study shows that CyDTA affects the coordination
structure around Ni atom during both the impregnationand drying process for the preparation of NiMo/Al2O3 andNiW/Al2O3 catalysts.
References[1] N. Koizumi et al., Prep. Pap. –Am. Chem. Soc. Dev.
Pet. Chem., 49 (3), 291, (2004).
[2] H. Itoh et al., J. Jpn. Petrol. Inst., Vol 47, No.4, 2004.
th[3] Kagaku Binrann 5 edition, Kiso-henn II, p.813.
* yamada@erec.che.tohoku.ac.jp

Table Structural parametersa of Ni-O shell derived from Ni K-edge EXAFS for NiW/Al2O3 and NiMo/Al2O3 catalysts
prepared with or without CyDTA after drying processnd
1st Ni-O shell
2 Ni-O shell
Rf /%
CN
R /nm
CN
R /nm
σ /nm
σ /nm
NiW
6.4
0.205
0.0078
1.3
CyDTA-NiW

6.00.205

0.00876.7

0.282

0.0074

1.3

NiMo

6.00.2060.0089

1.3

CyDTA-NiMo
5.9
0.206
0.00846.8
0.279
0.0083aCN, coordination number; R, interatomic distance; Debye-Waller like factor; Rf, R factor defined as2
2 1/2
Rf = [Σ{χobs (k) – χcal (k)} /Σ χobs (k) ]0.9

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