545475 Catalysis of Liquid-Metal Indium for Direct Dehydrogenative Conversion of Methane into Higher Hydrocarbons

Monday, June 3, 2019: 2:09 PM
Texas Ballroom D (Grand Hyatt San Antonio)
Yuta Nishikawa1, Ayumi Nakaya1, Hitoshi Ogihara2, Yuki Ohtsuka3, Akira Nakayama3, Jun-ya Hasegawa3, Shoji Iguchi1 and Ichiro Yamanaka1, (1)Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, Tokyo, Japan, (2)Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University, Saitama, Japan, (3)Institute for Catalysis, Hokkaido University, Sapporo, Japan

Catalysis of Liquid-Metal Indium for Direct Dehydrogenative Conversion of Methane into Higher Hydrocarbons

Yuta Nishikawa,a Ayumi Nakaya,a Hitoshi Ogihara,b Yuki Ohtsuka,c Akira Nakayama,c Jun-ya Hasegawa,c Shoji Iguchi,a Ichiro Yamanakaa,*

aDepartment of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology,2-12-1-S1-16, Ookayama, Meguro-ku, Tokyo, 152-8550, Japan

bDepartment of Applied Chemistry, Graduate School of Science and Engineering, Saitama University, 255, shimo-ookubo, Sakura-ku, Saitama, 338-8570, Japan

cInstitute for Catalysis, Hokkaido University, Kita 21, Nishi 10, Kita-ku, Sapporo, 001-0021, Japan

*Corresponding author: +81-3-5734-2144, E-mail address: yamanaka.i.aa@m.titech.ac.jp

Abstract: Dehydrogenative conversion of methane (DCM) is an attractive reaction. We already reported that liquid-metal indium supported on silica (In/SiO2) was an effective catalyst for DCM. Characterization studies and kinetic studies indicated that liquid-metal indium catalyzed cleavage of a C-H bond of methane and coupling methane to ethane selectively. In addition, conversion of ethane and temperature-programmed reaction in ethane (TPR-C2H6) suggested that indium did not activate both a C-H bond and a C-C bond of ethane. Indium has the unique catalysis to activate only a C-H bond of methane, therefore, selectivity to hydrocarbons was still high despite high temperature.

Keywords: Methane conversion, Liquid metal catalysis, Indium catalysis.

1. Introduction

Methane (CH4) is the main component of natural gas, which is an abundant energy sources in the earth. Most of CH4 is currently used to generate electric power and heat because it is difficult to convert CH4 to valuable compounds. Steam reforming of CH4 to syngas (CO + H2) and following catalytic reactions are only realized as industrial processes for utilization of CH4. These processes need large amount of energy and costs because of mult-step reaction. Therefore, direct conversion of methane to chemicals and liquid fuels is a promising way to utilize natural gas.

In dehydrogenative conversion of CH4, molybdenum/zeolite (Mo/zeolite) catalysts have been extensively studied and tested to overcome coke deposition[1,2]. Recently, a few new DCM catalysts were reported. For example, Guo et al. reported the Fe/SiO2 catalyst (single Fe sites in a silica matrix) to convert CH4 to ethylene, benzene and naphthalene at >1223 K[3]. We also reported the In/SiO2 catalyst to convert CH4 to ethylene, propylene and benzene[4]. CH4 conversion was 4.8% and selectivity to hydrocarbons was 75 % by the In/SiO2 catalyst at 1173 K. In this work, we study detailed reaction mechanisms for the DCM reaction on the In/SiO2 catalyst.

2. Experimental

The In/SiO2 catalyst was prepared by a conventional impregnation method. Indium nitrate hydrate was dissolved in deionized water and CARiACT Q-3 (SiO2 support) was added to the solution. The mixture was dried up at 393 K. This catalyst precursor was calcined at 773 K in air and was reduced with H2 at 873 K. The DCM reaction tests were conducted using a fixed-bed quartz reactor (I.D. 12 mm) with In/SiO2 (100 mg) and CH4 (1 atm, 10 mL min-1) was flowed. Hydrocarbons and H2 were analyzed by gas chromatographs or an online mass spectrometer. In the cases of conversion of C2H6, 5% C2H6/Ar (1 atm, 30 mL min-1) or 0.5% C2H6/H2 (1 atm, 20 mL min-1) was flowed. A Ni/SiO2 catalyst as a reference one was prepared from nickel nitrate hexahydrate using the same method.

3. Results and discussion

Fig1.pngFigure 1 (a)-(d) show the profiles of temperature-programmed reaction (TPR) from 323 K to 1173 K with 4 K min-1 monitored by a mass spectrometer. In the TPR using CH4 on In/SiO2 (a), formation of C2H6 (m/z = 30) was observed from 800 K. On the other hand, no formation of C2H6 on SiO2 (b).It was clear that indium catalyzed CH4 activation and propylene and benzene were successively produced following the C2H6 formation. In the TPR using C2H6 on In/SiO2 (c), significant products were not detected at 800 K. Formations of H2 (m/z = 2) and CH4 (m/z =16) were observed over 950 K, corresponding to conversion of C2H6 (m/z = 28, 30). In the case of SiO2 (d), similar profiles were observed except for hydrogen production which was slightly suppressed by In/SiO2. Figure 1 indicated that indium could activate a C-H bond of CH4, however, a C-H bond of C2H6 cannot.

Table1.pngTo obtain more information of indium catalysis, conversion of C2H6 in H2 was conducted. As references, results of no catalyst and Ni/SiO2 catalyst were shown in Table 1. Ni/SiO2 catalyst converted C2H6 into CH4 and coke, therefore, a C-C bond of C2H6 was cleaved. On the other hand, dehydrogenation

of C2H6 to C2H4 was mainly proceeded on In/SiO2.

The selectivities on In/SiO2 were very similar to that of no catalyst. This indicated that distributions were thermodynamically decided. Indium cannot activate C-H and C-C bonds of C2H6, therefore, carbon deposition was suppressed. In the presentation, DFT-calculation results will be discussed.

4. Conclusions

Results of TPR-CH4 and TPR-C2H6 on In/SiO2 indicated that indium could activate only a C-H bond of CH4 but not a C-H bond of C2H6. Additionally, indium cannot cleave a C-C bond of C2H6 from the results of conversion of C2H6. These unique catalysis of In/SiO2 for CH4 and C2H6 results in higher selectivity to hydrocarbons in the DCM reaction.

References

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2.       S. H. Morejudo, R. Zanon, S. Escolastico, I. Yuste-Tirados, H. Malerod-Fjeld, P. K. Vestre, W. G. Coors, A. Martinez, T. Norby, J. M. Serra, C. Kj_lseth, Science, 353 (2016) 563.

3.       X. Guo, G. Fang, G. Li, H. Ma, H. Fan, L. Yu, C. Ma, X. Wu, D. Deng, M. Wei, D. Tan, R. Si, S. Zhang, J. Li, L. Sun, Z. Tang, X. Pan, X. Bao, Science, 344 (2014) 616.

4.       Y. Nishikawa, H. Ogihara, I. Yamanaka, ChemistrySelect, 2 (2017) 4572.


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