Photon Factory Activity Report 2016 #34 (2017)

AR-NW10A/2014G060, 2013G197

XAFS study of Ru/K-Al2O3 catalyst functionalized by NHC ligands
for selective hydrogenation
Satoshi MURATSUGU*1, Fei WANG1, Mizuki TADA1,2
1

Department of Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602, Japan.
2
RCMS and IRCCS, Nagoya University, Furo-Cho, Chikusa-ku, Nagoya, 464-8602, Japan.

1 Introduction
N-heterocyclic carbenes (NHCs) were directly graftedon the K-doped Al2O3-supported Ru nanoparticle catalyst(Ru/K-Al2O3)[1] that was highly active for thehydrogenation reaction.[2] The oxidation state and local
coordination structures of NHC-modified Ru catalysts
were investigated by Ru K-edge XAFS. The switchoverof selectivity on the hydrogenation of phenylacetylene
was observed together with the amount of NHC that was
directly coordinated to Ru nanoparticle.[2]2 Experiment
Ru/K-Al2O3 (Ru: 4 wt%, K: 4 wt%) were preparedaccording to the literature.[1] The solution of NHC (1,3dicyclohexylimidazolium;ICy (1),1,3-bis(2,4,6trimethylphenyl)imidazolium; IMes (2)) was impregnatedto Ru/K-Al2O3. Ru K-edge XAFS was measured intransmission mode at 20 K at the NW10A station with aSi(311) double-crystal monochromator. The energy andcurrent of electrons in the storage ring were 6.5 GeV and60 mA, respectively. Ionization chambers filled with pureAr and pure Kr were used to monitor incident andtransmitted X-rays, respectively. EXAFS were analysedwith IFEFFIT (Athena and Arthemis) ver. 1.2.11. k3Weighted EXAFS oscillations were Fourier transformed
into R-space, and curve-fitting analysis was carried out inR-space. Fitting parameters were coordination number(CN), interatomic distance (R), Debye-Waller factor (σ2),
and correction of-edge energy (∆E0). Phase shifts andbackscattering amplitudes were calculated by the FEFF8code.
3 Results and Discussion
The local coordination structures of catalysts wereinvestigated by Ru K-edge EXAFS analysis, andstructural parameters are listed in Table 1. The ICyattached Ru/K-Al2O3 (Low ICy loading: 1@Ru/K-Al2O3,
the actual NHC loading was estimated by TGA) had RuRu interaction at 0.266 ± 0.001 nm (Coordination number(CN): 3.9 ± 0.8), and Ru-O/C interaction at 0.201 ± 0.002
nm (CN: 2.8 ± 0.7). These values were similar to those ofRu/K-Al2O3 without NHC functionalization (Table 1),
suggested that the modification of ICy did not change theRu nanocluster catalyst itself, although the only the direct
Ru-ICy bond was estimated by 13C SS-NMR spectra. The
little influence on Ru/K-Al2O3 after the attachment of ICyto Ru nanoparticle was also observed by Ru K-edge
XANES and TEM. The increase in the amount of
attached ICy on Ru/K-Al2O3 (1@Ru/K-Al2O3-HL), andthe usage of different NHC (2) (2@Ru/K-Al2O3,
2@Ru/K-Al2O3-HL) did not also affect the structure ofRu nanoparticle on Ru/K-Al2O3 (Table 1). The attachedstructure was different on the type of NHCs. Almost all of
1 was selectively coordinated on the surface of Ru
nanoparticles irrespective of the loading of 1. The
attachment of 2 on Ru/K-Al2O3 suggested the twodifferent coordinated structures on Ru nanoparticle with asmall amount of 2 attached on the K-Al2O3.
The catalytic hydrogenation performance ofphenylacetylene was dependent on the loading of 1/2. For
1@Ru/K-Al2O3 and 2@Ru/K-Al2O3, fully hydrogenatedproduct (ethylcyclohexane) was the major product (57%for 1@Ru/K-Al2O3 and 92% for 2@Ru/K-Al2O3);
however, for 1@Ru/K-Al2O3-HLand 2@Ru/K-Al2O3-HL,partially hydrogenated product (ethylbenzene) was themajor product. These results indicate that the type andloading of the NHC on Ru/K-Al2O3 can finely tune thechemoselective hydrogenation.
Table 1 Curve-fitting results of Ru K-edge EXAFS Fourier transformsof the Ru nanoparticle catalysts on K-Al2O3 (Ru: 4 wt%) aShellCNR /nm∆E0 /eVσ2 /× 10-5 nm2

Ru/K-Al2O3 (Rf = 2.3%)
Ru–Ru
3.9 ± 1.0
0.266 ± 0.001
2±210 ± 1
Ru–O
2.6 ± 0.8
0.200 ± 0.002
11 ± 46±2
1@Ru/K-Al2O3 (Rf = 1.7%)
Ru–Ru
3.9 ± 0.8
0.266 ± 0.001
3±29±1
Ru–O/C2.8 ± 0.7
0.201 ± 0.002
11 ± 46±2
1@Ru/K-Al2O3-HL (Rf = 1.0%)
Ru–Ru
4.2 ± 0.60.267 ± 0.001
3±19±1
Ru–O/C
2.5 ± 0.6
0.201 ± 0.001
11 ± 36±2
2@Ru/K-Al2O3 (Rf = 1.0%)
Ru–Ru
4.2 ± 0.7
0.266 ± 0.001
2±19±1
Ru–O/C2.6 ± 0.6
0.201 ± 0.002
10 ± 36±22@Ru/K-Al2O3-HL (Rf = 1.8%)
Ru–Ru
3.9 ± 0.9
0.266 ± 0.001
2±210 ± 1
Ru–O/C2.8 ± 0.7
0.201 ± 0.002
11 ± 46±2ak range and R range were 30-150 nm-1 and 0.13-0.30 nm, respectively.

References[1] S. Muratsugu, S. Kityakarn, F. Wang, N. Ishiguro, T.
Kamachi, K. Yoshizawa, O. Sekizawa, T. Uruga, M. Tada,Phys. Chem., Chem. Phys. 2015, 17, 24791-24802.
[2] J. B. Ernst, S. Muratsugu, F. Wang, M. Tada, F.
Glorius, J. Am. Chem. Soc., 2016, 138, 10718-10721.
(highlighted in SYNFACTS, 2016, 1313, and chosen as
Synfact of the month)* smuratsugu@chem.nagoya-u.ac.jp