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

9A, 7C/2003G067

XAFS characterisation of Pt and PtSn catalysts supported on carbon blackM.Carmen ROMÁN1*, Juan A. MACIÁ1, Diego CAZORLA1 Hiromi YAMASHITA2
1Dto. Química Inorgánica, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
2Div. of Materials and Manuf. Sci. Osaka University, 2-1 Yamada-oka. Suita, Osaka, 565-871 Japanof analogous samples prepared with activated carbon theeffect of the preparation method was more pronounced [2],probably because the support contains more surface
oxygen groups.
Reduced catalysts
Fig. 1 shows the FT-EXAFS profiles obtained for the
reduced samples Pt/V3G, PtSn/V3G (SI) and PtSn/V3G(CI) and for a platinum foil. Fig. 2 shows thecorresponding FT-EXAFS profiles of the analogous
catalysts prepared with activated carbon (AC) [2].
16
Pt foil

12Pt/V3G
PtSn/V3G(CI)10

PtSn/V3G(SI)8642001234

56r(A)
1614Figure 2Pt foil

12Pt/AC
PtSn/AC(CI)

10PtSn/AC(SI)a.u.

ExperimentalThe comercial carbon black V3G was used as support.
The catalysts were prepared using solutions of H2PtCl6
and SnCl2 following two procedures: i) successive
impregnation (first Sn and then Pt) (sample PtSn/V3G(SI)), and ii) coimpregnation (sample PtSn/V3G (CI)).
The desired Pt loading is about 1wt.% and the atomic ratio
Pt/Sn 1. A monometallic Pt/V3G was also prepared.
Drying and reduction were carried out at 383K (overnight)
and at 623 K (in H2 flow, 12 h), respectively. The PtIIIedge absorption spectra were recorded in the transmission
mode at RT (E=11300-12700 eV). A FT was performed
on k3-weighted oscillations over the range of 3-12 Å-1.

Figure 1

14a.u.

Introduction
Supported PtSn are effective catalysts fordehydrogenation or cyclization reactions [1]. The
properties and even the accesibility of the active phaseare strongly influenced by the nature of the support. We
have already investigated by XAFS the structure of theactive phase of PtSn catalysts supported on activatedcarbon and on SiO2 focusing the attention on thepreparation method and the temperature of reduction [2,3].
In the present work, the support of the catalysts studied iscarbon black. On this non-porous material the active phaseis expected to be more accesible to reactants. However,
because its surface chemistry is different from that ofactivated carbon, the properties of the active phasedeveloped are, as well, probably different.

864Results and discussion

2Dried catalysts
Probably due to the non-porous structure of the carbon
black, the amount of metals loaded is much lower than
expected:
PtSn/V3G (SI)……0.41wt%Pt and Sn/Pt= 0.17
PtSn/V3G (CI)…... 0.55wt%Pt and Sn/Pt= 0.08
The FT-EXAFS spectra obtained for the dried
catalysts contain a main maximum at about 2 Å,corresponding to Pt-Cl bonds. The intensity of thismaximum is lower than in the precursor compound,
H2PtCl6 according to a decrease and/or change in thecoordination of Pt due to the interaction of the platinum
precursor with surface oxygen groups and/or via a
reduction process in which carbon acts as a reducing agentand as a coordinating ligand. A slight effect of thepreparation method is observed being the modification of
the coordination sphere of Pt lower for the sample
prepared by successive impregnation (PtSn/V3G(SI)).
However, the analysis of the white line shows that in both
bimetallic PtSn and the monometallic Pt supported
catalyst the electronic density of Pt is similar. In the case00123456r(A)For both supports the FT-EXAFS data of thebimetallic samples show three maxima although withdifferent relative intensity. The asignation of thesefeatures to different Pt of PtSn is controversial [2]. At themoment, we are investigating this aspect by considering
the presence PtxSny alloys in the fitting calculations.
What is more remarkable is that even with thenoticeably low amount of Sn in catalysts prepared withV3G, PtSn species are developed. XPS of the PtSn/V3G
catalysts show that even with a total Sn/Pt close to 0.1,
there is a surface enrichment of tin (surface Sn/Pt about 3).
In the case of samples prepared on AC with Sn/Pt=1, thesurface Sn/Pt was about 20.
References[1] F.Pasos et al. J.Catal. 160, 106 and 118 (1996).
[2] M.C. Román et al. J.Jpn. Petrol. Inst., 47, (2004) 164.
[3] M.C. Román, PF user’s reports 2001, 2002, 2003.
*mcroman@ua.es

Users' Report189