Photon Factory Activity Report 2004 #22 Part B (2005)
Surface and Interface

10B, 9A, 9C, 7C/2002G274

In-situ XAFS measurement of Pd-Pt/SiO2 under HDS reaction conditions
Kyoko K. BANDO1*, Toshihide KAWAI 2, Kiyotaka ASAKURA3, Atsushi TAKAHASHI1,Noriyasu HAMAKAWA1, Juan Jose BRAVO SUAREZ1, Yuji YOSHIMURA1, andS. Ted OYAMA4
1
National Institute of Advanced Industrial Science and Technology, Tsukuba, 305-8569, Japan
2
Spring-8, JASRI, Koto, Mikazuki, Hyogo 679-5198, Japan
3
Catalysis Research Center, Hokkaido Univ., Sapporo, Hokkaido 001-0021, Japan
4 Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0211, USA

FT/a.u.

(a)0after reduction
HDS for 81 min
12 h24 h

24Distance / (0.1 nm)(b)
FT/a.u.

Introduction
Supported Pd-Pt catalysts are efficient catalysts forhydrodesulfurization (HDS) and hydrodearomatization(HDA) of diesel fuel. But their catalytic performance isclosely dependent on the support [1]. In our previous
work, in-situ XAFS (X-ray Absorption Fine Structure)measurements under HDS conditions were carried out for
an Al2O3 supported Pd-Pt (Pd-Pt/Al2O3) catalyst [2]. It
was found that the structure of the active phase was notidentical to that obtained after gas phase sulfidation, andthat sulfidation of Pd atoms proceeded more deeply under
HDS conditions. In this work, in-situ XAFS analysis of aSiO2 supported Pd-Pt (Pd-Pt/SiO2) catalyst was conducted
and the results are discussed in connection with thecatalytic activity.

6after reduction
HDS for 81 min
12 h
24 hExperimental
A SiO2 supported Pd-Pt catalyst was prepared by theincipient wetness impregnation method. The total metalcontent was 2 wt% and the atomic ratio of Pd/Pt was 4.
The impregnated sample was calcined under O2 at 573 Kfor 3 h. A round disk of calcined catalyst (60 mg, 8 mmin diameter) was placed in an in-situ XAFS cell [3].
Reduction of the sample was carried out under a flow of
100 % H2 gas at a flow rate of 50 ml/min at 573 K for 3 h.
After pretreatment, the HDS reaction was conducted at553 K under 4 MPa of total pressure. Hydrogen gas wassupplied at 40 ml/min and a model oil composed ofdibenzothiophene (500 ppm in sulfur), tetraline (30 wt %)and n-hexadecane (as solvent) was fed at a rate of 4 g /h.
The reaction was carried out for 24 h.
XAFS
measurements were carried out at BL10B for Pd K-edge
and at BL7C, 9A and 9C for Pt LIII-edge. All the spectra
were obtained by a step-scanning mode with a data
accumulation time of 0.5 – 1 s for each step. Analysis of
the data was conducted with commercially available
software (REX, Rigaku Co.). Parameters for the curvefitting analysis were extracted from spectra obtained forstandard substances at reaction temperature.

in the region from 0.16 to 0.3 nm. For the Pd K-edge theintensity of the metal-metal scattering peaks decreased
during the reaction, but no distinct peak appeared at 0.2nm, which could be assigned to the Pd-S scattering. No
evidence of Pd-S was found in the XANES (not shown),either. In the Pt LIII-edge, there was also no evidence ofPt-S observed, that is, the Pt-S scattering peak did notappear at 0.2 nm in Fig.1 (b), and Pt LIII-edge XANES
spectra did not show any notable change during HDS.
Taking into account the fact that the HDA activity of PdPt/SiO2 is much lower than that of Pd-Pt/Al2O3, it wassuggested that the surface of the metal particles of PdPt/SiO2 was covered with a rigid thin sulfide layer.

Results and Discussion
Fig.1 shows Fourier transformed EXAFS (k3χ(k))
spectra for (a) the Pd K-edge and (b) the Pt LIII-edge
observed during the HDS reaction. After reduction at 573
K, an intense peak due to metal-metal scattering appearedReferences[1] H. Yasuda, et al., Appl. Catal. A: General 185, L199 (1999).
[2] K. K. Bando, et al., PF Activity Report, 21, 75 (2004).
[3] T. Kawai, et al., Chem.Lett., in preparation.
* kk.bando@aist.go.jp

024Distance / (0.1 nm)

6Fig.1 Fourier transform of (a) Pd K-edge and (b) Pt LIII-edge
EXAFS spectra during HDS.

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