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

10B/2005G214

Nitriding process of Fe-promoted Nb/SiO2 catalyst prepared from peroxoniobic
acid as Nb precursor
Nobuyuki ICHIKUNI*1, Hiroari MATSUMOTO1, Yasuhiro
IWAMA1, Kyoko K. BANDO2, Shogo
1
SHIMAZU
1
ChibaUniversity,
Inage-ku,
Chiba 263-8522, Japan
2
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8569, Japan
Introduction
Early transition metal nitride (ETMN) was attractive asa new catalyst material due to the resemblance in physicalproperties to those of the group 8-10 metals. ETMNs
were usually prepared from the corresponding oxides
under the NH3 atmosphere at high temperatures. We have
tried to convert ETM oxide into ETMN without using
NH3 gas by the addition of Fe species.
In this study, the Fe added Nb/SiO2 catalysts wereprepared and the nitriding process in a N2-H2 mixed gas
flow was investigated by in-situ XAFS method.

the temperature maintaining step (T = 1173 K). The
conversion from Nb-oxide to Nb-nitride was occurred notduring TPR process but during temperature keeping
process. The growth of Nb-N peak in Fig (b) is faster (atthe initial stage of temperature keeping process) than thatin Fig (a), which suggests the effectiveness of the 2steps
TPR process for nitriding.

(a) Fe-NbN/SiO2 (1step)Experimental
Nb/SiO2 was prepared from peroxoniobic acid and SiO2
(Aerosil, #200) as a precursor and a support, respectively.
Fe was introduced by using Fe(acac)3. The loading of Nband Fe were regulated to be 6 wt% and 20 mol% (to Nbatom), respectively. The precursor oxide catalyst wasnitrided in N2-H2 mixed gas flow to produce Fe-NbN/SiO2
catalyst by following two types of TPR process; (1) the-1
sample was heated at a linear rate of 5 K·min to the final
temperature (Tnit), and (2) the sample was heated to 563 K
and maintained for 60 min and heated again to Tnit=1173
K. The catalyst prepared from the former and the latterprocess was denoted as Fe-NbN/SiO2(1step) and FeNbN/SiO2(2steps), respectively.
Nb K-edge XAFS spectra were collected at BL-10Bwith Si(311) channel cut monochromator in thetransmission mode. It takes about 10 min to collect aEXAFS spectrum. Catalyst was pressed into a selfsupporting pellet and transferred into the SUS cell, withAcrylic windows (2 mm thickness) at the both ends of theX-ray path. The in-situ XAFS spectra were collectedunder a flow of N2-H2 during TPR and analyzed by theprogram REX2000 (Rigaku Co.).
Results and discussion
Nb oxide in Nb/SiO2 (without Fe addition) was not
nitrided by treating with N2-H2 gas at 1273 K. By
introducing 5-20 mol% Fe into Nb/SiO2 catalysts andtreated with N2-H2 gas at 1273 K led to the formation
NbN species on SiO2. Moreover, the Tnit could be lowered
about 100 K, by using peroxoniobic acid as Nb precursor
instead of using NbCl5.
Figure shows the FT spectra of in-situ EXAFS duringnitriding process. The Nb-N peak at around 0.18 nm wasobserved for both catalyst. The intensity of Nb-(N)-Nbpeak at around 0.30 nm gradually became stronger during

at RT

T=
1173 K

TPR(b) Fe-NbN/SiO2 (2steps)

at RT
T=1173 K

TPR
0.00.1

0.2

0.3 0.4 0.5 0.6r / nm
Fig. FT of k3-weighted Nb K-edge in-situ EXAFS spectra
during nitriding process; (a) Fe-NbN/SiO2 (1step) and (b)Fe-NbN/SiO2 (2steps).

*ichikuni@faculty.chiba-u.jp

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