Photon Factory Activity Report 2017 #35 (2018)

BL-9C/2016G069

Promoting effect of the interfacial Ni-O-Si structure on silica supported NiOnanocluster catalyst for the 1-phenylethanol oxidation reaction
Takuro SASAKI, Nobuyuki ICHIKUNI*, Takayoshi HARA and Shogo SHIMAZU
Chiba University, Inage-ku, Chiba 263-8522, Japan

2 Experimental
SiO2 (Fuji Silysia Chemical Ltd., CARiACT P-10) or
activated carbon (Wako Pure Chemical Industries Ltd.)supported NiO catalysts were prepared by animpregnation
method.
NiO(amm)/SiO2-TandNiO(amm)/AC, NiO(ace)/SiO2-T and NiO(nit)/SiO2-T
were obtained by using [Ni(NH3)6](NO3)2, Ni(acac)2 andNi(NO3)2 as a precursor, respectively, followed by heat
treatment at T (K) in air. The heat treatment temperature
was altered as RT, 573, 673 and 773 K. Ni loading
amount was regulated to 5 wt%. Ni K-edge XAFS data
were obtained at PF BL-9C (Proposal No.: 2016G069) ofIMSS-KEK by using Si(111) double crystal
monochromator in a transmission mode at roomtemperature.
3 Results and Discussion
Figure shows Ni K-edge XANES of NiO catalysts andreference compounds. XANES shape of all catalysts (Fig.
c-h) was similar to that of bulk NiO (Fig. a). Additionally,NiO(amm)/SiO2-RT, -573 and -773 (Fig. f-h) showed twoshoulders at 8346 eV (peak α) and 8350 eV (peak γ)
besides peak β (at 8349 eV). Those two peaks werecharacteristic of nickel silicate as shown in Fig. b. This
result indicates that NiO and Ni-O-Si structure coexistedon NiO(amm)/SiO2-T catalysts. The ratio of Ni-O-Sistructure was lowered as increasing the treatment
temperature (Table 1).
Moreover, XAFS measurements revealed that theparticle size of NiO can be controlled by changing the Niprecursor, support and treatment temperature as shown inTable 1.
NiO nanocluster on the interfacial Ni-O-Si structure
showed higher activity than NiO nanocluster only did,which indicated that Ni-O-Si structure had the promoting
effect for this reaction and that effective contribution ofinterfacial Ni-O-Si structure was a key factor for thisreaction.

αNormalized absorption

1 Introduction
Support itself has some important roles on the solid
catalysis; maintaining the high surface area, stabilizing
the dispersion of active species during the catalysis.
Furthermore, the support can produce a synergy effectwith active species and promote catalytic reactions [1].
In this work, we tried to develop supported NiOnanocluster catalysts and to reveal its interfacial structure
by utilizing XAFS. As a consequence, promoting effectof the interfacial structure between NiO nanocluster andSiO2 for 1-phenylethanol oxidation reaction was found.

γβ832083408360
Photon energy / eV(h)
(g)
(f)
(e)
(d)
(c)
(b)
(a)

8380

Fig. Ni K-edge XANES spectra of NiO catalysts (c-h) andreference compounds (a, b): (a) bulk NiO, (b) bulk nickel
silicatea, (c) NiO(nit)/SiO2-673, (d) NiO(ace)/SiO2-673, (e)NiO(amm)/AC-573,(f)NiO(amm)/SiO2-773,(g)NiO(amm)/SiO2-573, (h) NiO(amm)/SiO2-RT. aPrepared by amethod reported in [2].
Table 1 Coordination number of Ni-Ni, ratio of Ni-O-Sistructure and yield of 1-phenylethanol oxidationa

Ni-O-Si ratioc
Yieldd (%)(%)
NiO(amm)/SiO2-RT
7.3
6351
NiO(amm)/SiO2-573
7.4
5228
NiO(amm)/SiO2-773
8.043
4.5
NiO(amm)/AC-573
5.0017
NiO(ace)/SiO2-673
7.00
7.8
NiO(nit)/SiO2-673
120
1.9a
1-Phenylethanol (1 mmol), NiO catalyst (0.10 g, S/C = 12),solvent: p-xylene (5 mL), atmosphere: O2 (1 atm), reaction
temperature: 373 K, reaction time: 6 h. bCoordination number ofthe nearest Ni-Ni coordination. cDetermined by XANES pattern
fitting analysis. dDetermined by gas chromatography using aninternal standard technique.
Catalyst

CNb

Acknowledgement
This study was supported by JSPS KAKENHI Grant
Number 23560928 and 26420784.
References[1] T. Sasaki et al., Catal. Today 307, 29 (2018).
[2] M.V. Sivaiah et al., Micro. Meso. Mater., 140, 69(2011).
* ichikuni@faculty.chiba-u.jp