Photon Factory Activity Report 2005 #23Part B (2006)
Surface and Interface

7C, 9C, 10B/2004G323

Development of Combined in-situ Analysis Technique - Simultaneous
Measurement of XAFS and IR Applied to Analysis of supported Pd-Pt Catalysts
Kyoko K. BANDO*1, Juan Jose BRAVO SUAREZ1, Hiroyuki IMAMI1, Motoyasu IMAMURA 1,2
3
Takeshi KUBOTA , Nobuyuki ICHIKUNI1Natioanl Institute of Advanced Industrial Science and Technology, Tsukuba, 305-8569, Japan
2
Shimane Univ., Matsue , Shiamne 690-8504 Japan
3Chiba University, Inage-ku, Chiba, 263-8522, Japan
Introduction
Supported Pd-Pt bimetallic catalysts are active forhydrodearomatization of diesel fuel due to the high sulfur
tolerance. However, it is still not clear how the Pd-Pt
bimetallic system obtained high tolerance against sulfur.
We have done in-situ XAFS studies of Pd-Pt catalysts andhave obtained some information about the structure ofactive phase.
But XAFS analysis gives averaged
information of all the metal species contained in thecatalysts. We need to know the structural information of
metal species on the outer surface, which really exposed
to sulfur. In this work, we combined in-situ FT-IR withXAFS. As in-situ FT-IR provides the information about
the structural change of adsorbed species, we compared
the results obtained by XAFS with FT-IR and tried toextract the structural information of surface species fromXAFS data.
Experimental
For the development of the simultaneous measurement
method of XAFS and IR, it is needed to adjust the IR
spectrometer to the equipment of XAFS beam lines. For
that purpose, we used a portable FT-IR (JASCO, VIR9500), which could lead an incident IR beam from themain machine to a sample compartment unit through an
optical fiber composed of ZnSe. An MCT detector wasattached to the sample compartment unit and the IR beam
was set to intersect the X-ray beam for XAFS
measurement at an angle of 90°(fig.1). The XAFS cell
had a cross shape equipped with 4 windows, which let
both X-ray and IR penetrate the cell at the same time.

MCT(insideof theBox)

The Pd-Pt catalysts
IRwere prepared using
Al2O3 as supports. The
X-ray
metal loading was 2 wt%
and the atomic ratio ofPd/Pt was 4.
TheSample
calcined catalyst wasFig.2 Diagram of thepressed into a pellet andsample setting inside ofset in the in-situ cell.
the cell
The amount required forEXAFS
measurement
2was about 0.38 g/ cm . However, for IR measurement, a2
disk should be thinner than 0.038 g/ cm . To make bothmeasurement possible at the same time, two disks withdifferent thickness was set in the center of the cell asshown in fig.2. The catalyst was treated in-situ underhydrogen at 573 K, and exposed to 20% CO/He at 323 K.
Then TPR (temperature programmed reduction) wascarried out under a flow of hydrogen from 323 K to 573
K at the ramp of 5 K/ min. During the TPR process, FTIR and XAFS measurement was conducted continuously
every two min. for IR and every 3 min. for XAFS.
Results and discussion
For Al2O3 supported Pd-Pt catalyst, adsorbed CO
species gradually desorbed with temperature upto 523 K,
no noticeable change was observed for the Pd K-edge
XANES spectra during TPR. Pt LIII-edge XANES(observed separately) also showed corresponding gradualchange. It is strongly suggested that Pt atoms werelocated on the outer surface of metal particles rather thanin the bulk.
1.0

X-ray

0.8
0.6
0.4
0.2

IR

11.550

OpticalFiber

Fig.1 In-situ XAFS and IR combined analysis system set at
BL10B.

66

Users' Report

11.555
Energy / eV

11.56011.565x103

Fig.3 Change in Pt LIII-edge XANES observed for Pd-Pt/Al2O3
during TPR.

* kk.bando@aist.go.jp