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

12C,NW2A/2005C010

In-situ XAFS observation of reduction of nickel oxides
Masao KIMURA*1, Akane SUZUKI2, Noriaki OHTA3, Yasuhiro NIWA2, Yasuhiro INADA2,and Masaharu NOMURA2
1Adv. Tech. Res. Lab., Nippon Steel Corp., Futtsu, Chiba, 293-8511, Japan2
Photon Factory, KEK, Tsukuba, Ibaraki, 305-0801, Japan
3
Nippon Steel Technoresearch, Chiba 293-8500, Japan
Introduction
Catalytic reforming of CH4 with CO2 to produce
synthesis gas has gained a growing interest recently,considering chemical utilization of natural gas and CO2[1]. Several nickel catalysts for the CO2 reforming havebeen developed. It has been reported that nickel magnesia
solid solution catalysts reduced at high temperature
showed excellent activity and stability for CO2 reformingof methane [2]. It has been shown that NiO/MgO catalyst
has excellent stability [3]. Reduction reaction of nickel
oxide and metal oxide including nickel is of a great
importance to research and develop nickel catalysts for
the CO2 reforming. In this study, in-situ XAFS (X-rayAbsorption Fine Structure) technique has been developed
to observe structure changes of nickel oxide in H2/He gas
at high temperatures.
Experiments
Figure1 shows the main part of a newly developed
reaction cell. The cell is made of stainless steel with
Kapton-film windows which X-ray beam can passthrough. Powder specimen was kept inside a holder in ashape of cylinder. The thickness of specimen is about 4mm.
The holder was sealed in the center of the cell. The
specimen was heated up to ca. 1073 K by rod heaters
located above the specimen under a flow of H2/He gas.
The temperature of the specimen was monitored with athermo-couple located above the specimen holder.
NiO powder was mixed with BN powder to obtain
XAFS spectra with high quality and packed inside theholder. The specimen was heated in a gas of
3%H2/97%He with a flow rate of 200 ml/min. XAFS
spectra at Ni K-edge were measured in a transmisssion
geometry at BL-12C and NW2A at PF, KEK, Tsukuba,Japan.
Results and Discussion
XAFS spectra were observed at different times: t after
the temperature reached a specific temperature. Nodifference was observed among spectra of t = 5, 10, 20
and 40 min. at all temperatures.
Figure2 shows the radial distribution function (RDF)
around Ni obtained by in situ measurements at t = 5 min.
RDF before heating shows that the specimen is in thestate of NiO. As the temperature increases, peakintensities corresponding to NiO decrease and those of Ni
metal increase. Near T= 983K, peaks corresponding to Ni

metal were clearly observed in RDF. At T= 1073K, only
peaks corresponding to Ni metal were observed in RDF.
After experiments, microstructures of the specimen
were observed with SEM and TEM. The specimen heated
up to T= 1073K contains fine grains of Ni metal with asize less than 1.0 µm in diameter among BN grains. There
was no clear indication of reaction between Ni and BNgrains.
It can be concluded that the reduction of NiO to Ni in aflow of H2/He gas can be clearly observed by the newsystem. The reduction reaction completes at T = ca. 1073
K. Mixture of NiO with BN has no detectable effects onreduction reaction.
This system is being applied to Ni base catalyst.
Combination of this system with quick-XAFS may be
powerful to observe dynamics of reduction of Ni basecatalyst and formation of Ni nano particles.

Fig. 1 The main part of a newly developed reaction cell.

Fig. 2 Change of RDF around Ni obtained by in situ
measurements during heating in H2/He gas.
References[1] B. Delmon, Appl. Catal., B1, 139 (1992).
[2] K. Fujimoto et al, Energy Conversion andManagements, 33, 529 (1992).
[3] Y. H. Hu and E. Ruckenstein, J. Catal., 163, 306 (1996).

*kimura@re.nsc.co.jp

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