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

10B/2003G297

Coordination structure around Mo and W atoms of NiMo and NiWhydrodesulfurization catalysts during their preparation steps
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 activities to meet severe
regulations for the sulfur content of the transportation
fuels.
Recently, the authors found that the addition of somechelating 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 the impregnation anddrying process and eventually affects the sulfide
structures [2]. In the separate report, we showed thatCyDTA affects the coordination structure around Ni atom
during both the impregnation and drying process for thepreparation of NiMo/Al2O3 and NiW/Al2O3 catalysts by
Ni K-edge EXAFS. Here, we have also reported Mo Kedge and W LIII-edge EXAFS spectra of these catalysts
during the preparation steps.
Experimental
Mo K-edge and W LIII-edge EXAFS spectra for
NiMo/Al2O3 and Ni/W/Al2O3 catalysts after drying andimpregnating steps were measured at room temperature ina transmission mode at BL10B and BL12C. After the3background subtraction, k -weightened EXAFS functions
were Fourier transformed into a R space and then curvefitting analyses were carried out in the R space.
Backscattering amplitude and phase shift for W-O bond inpolycrystalline WO3 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 W LIII-edge EXAFS spectrum for
NiW/Al2O3 catalyst prepared without CyDTA afterimpregnation process shows only one W-O shell as shownin Fig. 1. Because the interatomic distance of this shell(0.177 nm, see Table) matched well with that for W-Obond in WO3 (0.177 nm), it is suggested that WO6 species
with an octahedral coordination is a predominate species
formed on Al2O3 after the impregnation. The subsequent
drying process hardly affects its coordination structure asshown in Table.
When NiW/Al2O3 catalyst was prepared with CyDTA,
we also observed one W-O shell in Fourier transformed
spectra after the impregnation and drying process. Boththe interatomic distance and the coordination number ofthis shell are consistent with those observed in the spectra
for the catalyst without CyDTA (Table). In the case ofNiMo/Al2O3, we could not find a significant difference inFourier transformed spectra for the catalyst prepared withand without CyDTA. Therefore, it can be concluded thatCyDTA has little influence on the coordination structurearound Mo and W atoms of NiMo/Al2O3 and NiW/Al2O3catalysts during the preparation procedures.
66ab4

4

2

2

00-2-2-4-4
00.1

0.2 0.3 0.4 0.5
Bond length /nm

0.600.10.2 0.3 0.4 0.5
Bond length /nm

0.6

Fig.1 Fourier transformed EXAFS spectra for NiW/Al2O3
catalyst prepared without CyDTA after impregnation (a)and drying (b) process.
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.
* yamada@erec.che.tohoku.ac.jp

Table Structural parametersa of W-O shell derived from W LIII-edge EXAFS for NiW/Al2O3 catalysts prepared withor without CyDTA
Prepared with CyDTA
Prepared without CyDTA
CN
R /nm
/nm
CN
R /nm
/nm
After
4.7
0.177
0.00855.2
0.177
0.0086
impregnation
After drying
4.4
0.178
0.00815.0
0.177
0.0075a256

CN, coordination number; R, interatomic distance; Debye-Waller like factor

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