Photon Factory Activity Report 2016 #34 (2017)

AR-NW10A/2016G518

Local Structure around Zr Species in SiO2 Doped with Zr
Yuki Kato1,* and Shigeru Sugiyama2,*MMA Group, Otake R&D Center, Mitsubishi Chemical Co., 20-1 Miyuki-cho, Otake-shi,
Hiroshima, 739-0693, Japan2
Department of Applied Chemistry, Graduate School of Technology, Industrial and Science,
Tokushima University, Minamijosanjima, Tokushima, 770-8506, Japan
1

1 Introduction
Acidic catalysts are widely used for petroleum refineryand organic synthesis of bulk and fine chemicals [1,2].
This study was made to find out correlation between thestate of dispersing or aggregating and acidity on complexoxide (SiO2-XOa) doped other metal oxide (XOa) in SiO2.
We have found out that SiO2-ZrO2 have good acidity,
which changed by preparation methods and amount ofdoped zirconium. In the present report, zirconia supported
on SiO2 will be examined using XAFS in order tounderstand the local structure around zirconium.
2 Experiment
SiO2-ZrO2 were prepared via an impregnation method
using aqueous zirconium nitrate and SiO2. In the presentstudy, two atomic ratios of Zr/Si (0.004 and 0.007) inSiO2-ZrO2 are employed for XAFS analysis. As reference
samples, monoclinic ZrO2 and perovskite-type SiZrO3were used.
Analysis of XAFS near Zr-K edge was carried out atthe High Energy Accelerator Research Organization Witha storage ruing current of 400 mA (6.5 GeV). The X-rays
were nonochromatized with Si(311) at an NW10A station.
The absorption spectra were observed using ionizationchambers in the transmission mode. The photon energy
was scanned in the range of 17,498.90-19,098.90 for theZr-K edge.
The average coordination number was estimated fromthe comparison of XANES spectra of these two samples
and pattern-fitting analysis of EXAFS of both samples
referring the data for ZrO2 and SiZrO3.
3 Results and Discussion
Monoclinic ZrO2 and perovskite-type SrZrO3 used as
reference samples possess 7-coordinated and 6coordinated structures with lattice oxygen. XAFS spectraof SiO2-ZrO2 (Zr/Si = 0.004 or 0.007) were similar to thatof SrZrO3. Therefore, the local structure around Zr inthese SiO2-ZrO2 is dissimilar to that in monoclinic ZrO2
while seems to be similar to that perovskite-type SiZrO3
that is 6-coordinated structures with lattice oxygen, that is,oxygen octahedron structure.
It should be noted that the increase of Zr/Si ratios in
SiO2-ZrO2 resulted in the enhancement of peak intensity
due to monoclinic ZrO2. These results indicate that thelocal structure around Zr of SiO2-ZrO2 (Zr/Si = 0.004 or0.007) may be present between 6- and 7-corordinatedstructure with lattice oxygen.

Table 1 showed the average coordination number
estimated from the pattern-fitting analysis using XANESof both SiO2-ZrO2 and those of the reference samples(ZrO2 and SrZrO3). In Table 1, catalytic activity ratio andthe corresponding selectivity of aldol condensation werealso described. As shown in Table 1, it was further
supported that the increase of Zr/Si ratio resulted in theenhancement of the average coordination number. Inusing Zr-SiO2 (0.004 and 0.007), the catalytic activity forthe production of a chemical that proceeded on acidic
catalyst was examined. Although the enhancement ofZr/Si ratio in SiO2-ZrO2 resulted in the same activity ofthe reaction, under the same conversion level, theselectivity on SiO2-ZrO2 (0.004) was evidently greaterthan that on SiO2-ZrO2 (0.007).
Therefore it can be estimated in the present study thatthe enhancement of Zr/Si ratio in SiO2-ZrO2 did notcontributed to the enhancement of the catalytic reactivity
in the present system, while the presence of 6-coordinatedstructure such as perovskite-type SiZrO3 may be needed
for the catalytic reaction.
The enhancement of the 6-coordinated structure in
SiO2-ZrO2 may be next target to obtain the great activity
on the present catalyst system.
Table 1: Average coordination number and thecorresponding catalytic activity
Average
Catalytic
Zr/Si
Selectivity
coordination
activity
Inratio
numberratio
Zr-SiO2
0.004
6.29
1.00
1.00
0.007
6.38
0.99
0.96
References[1] J. N. Chheda, G. W. Huber, and J. A. Dumesic, Angew.
Chem. Int. Ed., 46, 7164-7183 (2007)[2] Reza Sadeghbeigi, Fluid Catalytic Cracking
Handbook, 2nd Edition, Chapter 3, p84, ButterworthHeinemann (2000)[3] S. Damyanova, P. Grange, and B. Delmon, J. Catal.
168, 421 (1997)[4] Q. Zhuang and J. M. Miller, Appl. Catal. A, 209, pL1L6, (2001)* sugiyama@tokushima-u.ac.jp