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

7C, 10B/2003G065

Effects of the supports in Pt-catalysts on dehydrogenation of decalin
Chiaki SHINOHARA, Satoshi KAWAKAMI, Kei-ichiro MURAI, Toshihiro MORIGA,
Shigeru SUGIYAMA*
Department of Chemical Science and Technology, Faculty of Engineering,
The University of Tokushima, Minamijosanjima, Tokushima 770-8506, Japan
Introduction
As a key technology for hydrogen supply to fuel cellvehicles, the combination of decalin/naphthalene system
has been proposed as an effective hydrogen carrier. Inour previous paper [1], it has been revealed that catalytic
active sites on Pt/C, which was prepared with the active
carbon support treated with NaOH and showed great
activities for the dehydrogenation of decalin tonaphthalene, are non-metallic Pt species. In the present
report, the dehydrogenation of decalin to naphthalene has
been investigated on Pt/C, Pt/Al2O3 and Pt/Al(OH)O inorder to examine the effects of the supports on thecatalytic activities and active sites over those catalysts.
Experimental
Commercially available 5 wt.% Pt/C (Aldrich) and 1Thewt.% Pt/Al2O3 (Aldirich) were employed.
preparation procedure of 1.46 wt.% Pt/Al(OH)O is asfollows. Boehmite (Al(OH)O) was prepared from sol-gel
method with aluminum iso-propoxide. Precursor of Pt
species (K2PtCl4 (Wako)) was impregnated on Al(OH)O,
followed by the reduction with aqueous solution ofNaBH4 (Wako) at 363 K. The surface areas of 5 wt.%
Pt/C, 1 wt.% Pt/Al2O3 and 1.46 wt.% Pt/Al(OH)O were21445, 286 and 170 m /g, respectively. X-ray absorption
fine structure (XAFS) near Pt L3-edge was measured (2.5GeV) with a storage ring current of 340 mA at the HighEnergy Research Organization.
The X-rays weremonochromatized with Si(111) and Si(311) crystals atBL-7C and BL-10B station, respectively. And theabsorption spectra were observed using ionizationchambers in a transmission mode. Batch-wise catalytic
dehydrogenation of decalin (1 or 1.25 ml) was examinedwith 0.3 g of Pt/C or 1.0 g of Pt/Al2O3 and Pt/Al(OH)O,
respectively, at 483 K under reactive distillation
conditions. Under those conditions, 0.015, 0.010 and0.0146 g of Pt spices were contained in the systems withPt/C, Pt/Al2O3 and Pt/Al(OH)O, respectively.
Results and Discussion
The dehydrogenation behaviors on the commerciallyavailable Pt/C, Pt/Al2O3 and Pt/Al(OH)O were describedin Fig. 1. Although the rather similar contents of Pt
species in those systems and the dissimilar surface areasof those three catalysts are evident, it is of interest to notethat hydrogen evolution from decalin after 150 min are
rather identical. Therefore the nature of Pt species isstrongly influenced by the supports.

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Users' ReportFig. 1: Dehydrogenation of decalin at 483 K.
From XAFS analyses, the nearest-neighbor distances ofPt-Pt in Pt/Al2O3 and Pt/Al(OH)O were 0.283 and 0.279
nm, which were corresponding to that (0.280 nm) in Pt
foil, indicating that the nature of Pt species in thosecatalysts is essentially identical to that of metallic Pt.
However the rather shorter Pt-Pt distance (0.259 nm) wasobtained from the commercially available Pt/C. As
shown in our previous study [1], the nearest-neighbordistance of Pt-Pt in active Pt/C prepared with active
carbon treated with NaOH solution was 0.265 nm whilethat in non-active Pt/C prepared with the support nottreated with NaOH was 0.280 nm. Those results from theactive Pt/C indicate that the high dispersion of Pt affords
a more covalent species, resulting in the great activities
for the dehydrogenation of decalin. Based on thoseprevious results, present XAFS analyses of thecommercially available Pt/C reveal that Pt species withcovalent nature are also present on the commercial Pt/Ccatalysts. It should be noted that metallic Pt species inPt/Al2O3 and Pt/Al(OH)O afforded the corresponding
activities to those of Pt/C catalysts, indicating that theinteraction of Pt species and the support contributes to theactivities together with the nature of the catalytic activespecies.
References[1] C. Shinohara et al., Appl. Catal. A: Gen., 266, 251(2004).
* sugiyama@chem.tokushima-u.ac.jp