Photon Factory Activity Report 2019 #37 (2020)

NW-10A/2018G615

In situ XAFS Study on In/SiO2 Catalyst for Non-Oxidative Coupling of Methane
Dynamic Structure Change during the Activation Process
Upendar Kashaboina1, Yuta Nishikawa2, Yuki Wakisaka1 Natee Sirisit1, Deling Bao1, Hiroko ArigaMiwa1, Satoru Takakusagi1, Yuta Inami2, Fumiya Kuriyama2, Arnoldus Lambertus Dipu2, Hitoshi
Ogihara3, Shoji Iguchi2, Ichiro Yamanaka2, Takahiro Wada4, and Kiyotaka Asakura*1*1 Institute for Catalysis, Hokkaido University, Sapporo, 001-0021, Japan*2 Tokyo Institute of Technology, Tokyo, 152-8552, Japan*3Saitama University, Shimo-ookubo, 338-8570, Japan
4* Tokyo Medical and Dental University, Yushima, Tokyo, 113-8549, JapanThe structure of In /SiO2 catalyst for the non-oxidative coupling of methane(CH4)was studied by in situ X-ray absorption
fine structure (XAFS) during the activation process under CH4 flow. We found a drastic morphological change during theactivation process under CH4 flow such as melting to liquid at 430 K, the formation of a new structure with In-X(X=C orO) bond at 873 K and In metal reproduction at the reaction conditions at 1173 K.
1 Introduction
A catalyst for non oxidative coupling of methane(CH4)to higher hydrocarbons (NOCM) is important to use theCH4, a main ingredient of natural gases as feedstock. TheIn supported on SiO2 is an active catalyst for the NOCM
reaction[1]. Systematic studies of In/SiO2 using in situ
XAFS methods are required to gain further insights into
the structural changes of In/SiO2 during the activation
process in order to reveal the active site. The main purposeof this work is to investigate the structural change during
the activation process of the In/SiO2 under the CH4 flow
conditions using the in situ XAFS spectroscopy.[2]2 Experimental
An impregnation method was applied to the synthesis ofIn/SiO2 catalysts according to the reported way[1]. The In
K-edge spectra were calibrated against In metal foil withthe maximum in the first derivative of the K-edge set to27.94 KeV. Operando XAFS measurements of In/SiO2
were carried out in a transmission mode at the beamline
NW-10A, KEK-IMSS-PF (Tsukuba, Japan) using a Si(311) double crystal monochromator. All XAFS
experiments were recorded with 40 s time intervals from300 K to 1173 K under the CH4 flow conditions.
3．Results and discussion
Figure 1 represents the Fourier transforms(FT) of k3weighted ꭓ(k) signals at the In K-edge of the In/SiO2 under
the CH4 flow activation. The sudden change in the XAFS
oscillation was found at ~ 430 K where the peak top wasshifted to the lower side, indicating that In was melt toliquid. We found another prominent peak at ca. 873 K atca. 1.56 Å in the FT, indicating that the formation of In -X(X is a lighter element such as carbon or oxygen) [2]. At
the reaction temperature (1173 K), the In-X peak
disappeared, and the only In-In bond was found indicatingthat metallic In was reproduced.
The In/SiO2 catalyst exhibits the high catalytic

activity for NOCM in the CH4 flow activation process.
In situ XAFS revealed the melting of In metal at 473 K,

In-X(X=O,C) formation at 873 K. The reproduced In
metal at 1173 K was the active structure for NOCM
reaction. In catalyst was activated after the dynamic
structure changes.
1) Nishikawa,Y.; Ogihara, H.; Yamanaka, I.,
ChemistrySelect 2017, 2 (16), 4572-4576.
2) Kashaboina, U.; Nishikawa, Y.; Wakisaka, Y.; Sirisit,N.; Nagamatsu, S.; Bao, D.; Ariga-Miwa, H.;
Takakusagi, S.; Inami, Y.; Kuriyama, F.; Dipu, A. L.;
Ogihara, H.; Iguchi, S.; Yamanaka, I.; Wada, T.;
Asakura, K., Chem. Lett. 2019, 48 (9), 1145-1147.
Research Achievements
1. High temperature XAFS studies under the realworking conditions were successfully carred out
2. Dynamic change of In catalyst was revealed during
the activation process.
3. Active site structure was determined.
askr@cat.hokudai.ac.jp

Figure 1: k3-weighted EXAFS χ(k) signals during
the activation conditions under CH4 flow, atdifferent temperatures; (a) 300 K, (b) 473 K, (c) 873
K, (d) 1173 K