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

7C, 10B/2005G029

Effects of the incorporation of calcium into magnesium pyro-vanadate on theoxidative dehydrogenation of propane and the local structure around vanadium
Shigeru SUGIYAMA*1,2,3, Kazuya FUKUTA1, Masahiko 1,3
YOKOYAMA1, Kei-ichiro MURAI1,3,
Toshihiro MORIGA
1
DepartmentofAdvanced
Materials, Institute of Technology and Science,2
Department3 of Geosphere Environment and Energy, Center for Frontier Research of Engineering,
Department of Chemical Science and Technology, Faculty of Engineering,
The University of Tokushima, Minamijosanjima, Tokushima 770-8506, Japan
Introduction
Magnesium pyro-vanadate (Mg2V2O7) is one of theactive catalysts for the oxidative dehydrogenation ofpropane to propylene. The ease of removal of the latticeoxygen from the catalyst explains the great activities forthe oxidative dehydrogenation [1]. Although thecontribution of the lattice oxygen to the oxidation of
propane is evident, the influence of component divalentcation on the oxidation and the structure is still unclear. In2+
the present report, Ca -incorporated Mg2V2O7 isemployed for the oxidative dehydrogenation of propane2+
and the effect of the incorporation of Mg on the local
structure around vanadium is analyzed by X-ray
absorption fine structure (XAFS). Furthermore the XAFS
results
obtainedfromcalcium
hydroxyapatite(Ca10(PO4)6(OH)2) partly substituted with vanadate (VCaHAp), which showed great activities for the oxidative
dehydrogenation of propane [2], are also described.
Experimental
Magnesium pyro-vanadate that incorporated Ca2+,
which are denoted as Mg2-xCaxV2O7, was prepared fromMg(OH)2, Ca(OH)2 and NH4VO3 as shown in the previous
report on magnesium vanadates [1]. The preparation of VCaHAp was prepared with the preparation proceduredescribed in our previous paper [2]. Fixed-bed continuous
flow reactor operated at atmospheric pressure wasemployed for the catalyst activity test under the following
conditions: T=723 K, W=0.5 g, P(C3H8)=14.4 kPa,P(O2)=4.1 kPa and F=30 ml/min. X-ray absorption finestructure (XAFS) near V K-edge was measured (2.5 GeV)
with a storage ring current of 353-418 mA at the HighEnergy Research Organization. The X-rays weremonochromatized with Si(111) at BL-7C station. Theabsorption spectra were observed using ionizationchambers in a transmission mode.
Results and Discussion
The
catalytic
activities
fortheoxidative
dehydrogenation of propane on Mg1-xCaxV2O7 and VCaHAp together with Mg2V2O7 were described in Table 1.
As expected, the acceptable conversion of C3H8 together
with the great selectivity to C3H6 was observed onMg2V2O7. On Mg2-xCaxV2O7, the decrease and the increaseof the conversion of C3H8 and the selectivity to C3H6,2+
respectively, with increasing Ca -content in the catalyst

128

Users' Reportwere observed. On V-CaHAp, comparable activities forthe formation of C3H6 to those on Mg2V2O7 were observed
while the activities were strongly influenced by V-content
in the catalysts.
Table 1. Activities on Mg1-xCaxV2O7 and V-CaHAp
CatalystConversion (%) Selectivity (%)
C3H6 CO CO2
C3H8 O2
Mg2V2O7
14.0 87
50.9 29.3 19.8
7.7 3664.4 20.4 15.2
Mg1.90Ca0.10V2O7
5.1 3976.8 12.8 10.4
Mg1.80Ca0.20V2O7
V-CaHAp (V/P=0)
7.6 70
3.5 46.6 49.8
V-CaHAp (V/P=0.05) 17.2 89
52.4 27.5 20.2
V-CaHAp (V/P=0.10) 12.5 92
58.5 21.3 20.2
It should be noted that the mobility of the latticeoxygen was strongly influenced by the incorporation of2+
Ca into Mg2V2O7 and vanadate into CaHAp (not shown).
2+
Therefore the influence of the incorporation of Ca toMg2V2O7 and that of vanadate to CaHAp on the activities
and the mobility of lattice oxygen were evident. However2+
it is not clear that Ca and vanadate are certainly
2+
incorporated into the corresponding site: Mg site in3Mg2V2O7 and PO4 site in CaHAp since XRD patters ofMg2-xCaxV2O7 and V-CaHAp were essentially identical toMg2V2O7 and CaHAp. The nearest-neighbor distances
around V in Mg2V2O7 and Mg1.80Ca0.20V2O7, that were
calculated from XAFS data, were 0.175 and 0.177 nm,
respectively, indicating that the distance of V-O became2+longer after the incorporation of larger Ca into Mg2V2O7,2+2+indicating that Mg is certainly substituted by Ca [3].
However XAFS analysis of V-CaHAp could not becarried out since the absorption intensity was notsufficient. The employment of the fluorescence mode may
be needed for the analysis of V-CaHAp.
References[1] S. Sugiyama et al., Catal. Lett. 89, 229 (2003).
[2] S. Sugiyama et al., Catal. Lett. 103, 121 (2005).
[3] K. Inumaru et al., J. Chem. Soc. Faraday Teans.
88,625 (1992).
* sugiyama@chem.tokushima-u.ac.jp