Photon Factory Activity Report 2005 #23 Part B (2006)
Chemistry

9C/2005G041

Characterization of the K-Pt/Al2O3 Catalyst
for Preferential CO oxidation
Masatoshi KURIYAMA*1, Yuji MINEMURA1, Shin-ichi ITO1,Kazu OKUMURA2, Keiichi TOMISHIGE1, Kimio KUNIMORI1
1
Institute of Materials Science, Univ. of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan2
Department of Materials Science, Tottori Univ., Koyama-cho, Minami, Tottori 680-8552, Japan
have used only Pt-Pt species was enough to fit the spectra.
There was no contribution of Pt-O, and the contributionof Pt-Pt became larger than that with Pt/Al2O3 catalyst,
and this suggests that some amount of Pt particles
aggregated. Similarly, Pt particle was observed (2 nm) ofTEM [1]. From TEM observation, Pt particle in KPt/Al2O3 (10) were estimated to be 2 nm, whichcorresponds to 0.55 dispersion. We also calculated thesize of Pt particles by measuring the amount of COadsorption. From the result of CO adsorption, thedispersion of Pt in K-Pt/Al2O3 (10) should be smaller than0.55. This difference suggests that the surface of Pt metal
particle can be covered with potassium ion.
Although the addition of potassium ion caused thedecrease in the number of active site due to covering thesurface of Pt, catalytic performance for the PROX wasenhanced by the modification of the surface structure of
the Pt particles.
The results of EXAFS analysis support that more
effective active site on Pt particle for the PROX must beformed by the addition of potassium ion.

5|F(r)|Introduction
Hydrogen is a promising energy carrier related to thefuel cell technology, and generally hydrogen can beproduced by the reforming of methanol and hydrocarbons.
In this case, the produced gases always contain someamounts of CO. Preferential CO oxidation (PROX) in H2
rich mixtures is an important reaction in the fuel cell
technology in term of the purification of the fuel gas.
Recently, our group has reported that K-Pt/Al2O3 wasvery effective in the PROX reaction [1]. In this research,
we have carried out the characterization of K-Pt/Al2O3.
Experimental
The Pt/Al2O3 catalyst was prepared by impregnation theAl2O3 support with an aqueous solution of Pt(NO2)2(NH3)2(Soekawa). After the impregnation, the sample was driedat 383 K for 12 h, and then calcined in the air at 773 K for
1 h. The loading amount of Pt was 2 wt%. The Pt/Al2O3
catalyst modified with potassium ion was prepared, by thefollowing method. After the impregnation with aqueous
solution of Pt(NO2)2(NH3)2, the sample was dried at 383 K
for 12 h. And then the sample was impregnated again
with an aqueous solution of KNO3 (Wako), dried at 383 K
for 12 h, and calcined at 773 K for 3 h. The loadingamount of potassium ion is described in the molar ratio toPt (K/Pt) with the ratio of 10 (denoted as K-Pt/Al2O3(10) ).
The catalyst was crushed and pressed to the disk (0.5mm thickness, 10 mmφ) for EXAFS measurements. The
samples were pretreated at 773 K under H2 flow for 1 h.
After the treatment, the sample disk was transformed tothe measurement cell without exposing to air. Pt LIII-edge
EXAFS spectra were measured by transmission mode at3room temperature. After back ground subtraction, kweighted EXAFS functions were Fourier transformed into
R space and the one or two-shell fitting were analyzed bycurve fitting.
Results and Discussion
Fig. 1 shows the Fourier transform of EXAFS for
Pt/Al2O3 (a) and K-Pt/Al2O3 (10) (b). And table 1 shows
the fitting results of EXAFS data. From the fitting resultof EXAFS data of Pt/Al2O3 catalyst, we Pt-Pt and Pt-O
species were necessary for the good agreement.
Contribution of Pt-O is quite small and that of Pt-Pt islarge. The contribution suggests that Pt particle has astrong interaction with Al2O3 support. In addition, fromthe result of TEM observation, Pt particles were highly
dispersed and could not be observed (<1 nm). On theother hand, in the case of K-Pt/Al2O3 (10) catalyst, we(b) K-Pt/Al2 O3 (10)(a) Pt/Al2 O30123456Distance / 0.1 nm

Fig. 1 Fourier transform of EXAFS(a) Pt/Al2O3, (b) K-Pt/Al2O3 (10)Table1 EXAFS Parameters of Pt-Pt Shell and Pt-O Shell
Catalyst

Shells

CNR / 10-1 nm

σ / 10-1 nm

Pt/Al2O3Pt-Pt
Pt-O

5.8±0.8
0.5±0.22.65±0.008
2.04±0.022

0.094±0.008
0.050±0.045

Pt-Pt

8.5±0.5

2.74±0.003

0.079±0.003

K-Pt/Al2O3(10)

Reference[1] Y. Minemura et al. Chem. Commun., (2005) 1429
*s-k-m-8783@ims.tsukuba.ac.jp

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