545371 Low-Temperature Catalytic Oxidative Coupling of Methane over Ce-W-O System Catalysts in the Electric Field

Monday, June 3, 2019
Texas Ballroom Prefunction Area (Grand Hyatt San Antonio)
Yuna Takeno, Shuhei Ogo, Ayaka Sato, Tomohiro Yabe and Yasushi Sekine, Applied Chem., Waseda Univ., Tokyo, Japan

Direct catalytic conversion of methane to ethylene by oxidative coupling of methane (OCM) is attracted our attention. However, OCM reaction demands high temperatures over 973 K because of the stable structure of methane. At such high temperature, non-selective oxidation cannot be avoided, which greatly reduces C2 hydrocarbon selectivity. To solve this problem, we adopted a novel catalytic system, a catalytic reaction in an electric field, to activate methane at low temperature, such as 423 K. We previously reported that CeO2 supported tetrabutylammonium salt of Keggin-type phosphotungstate (TBA-PW12O40/CeO2) showed high OCM activity in the electric field even at 423 K. The purpose of this report is to investigate active site structure for OCM reaction in the electric field at low temperature, and to evaluate contribution of an electric field to OCM activity.TBA-PW12O40/CeO2 after reaction in the electric filed was characterized with Raman spectroscopy. It showed the peaks of TBA-PW12O40 disappeared and the peaks of Ce2(WO4)3 and WO3 appeared. Therefore, catalytic activity tests of Ce-W-O system catalysts were conducted in the electric field. From the activity tests, Ce2(WO4)3/CeO2, Ce2(WO4)3 and WO3/CeO2 showed OCM activity while WO3 did not showed OCM activity. Then, the catalysts before and after reaction were characterized by Raman spectroscopy. The Ce2(WO4)3/CeO2, Ce2(WO4)3 and WO3/CeO2 catalysts after reaction had the Ce2(WO4)3 structure, however the WO3 catalyst after reaction retained the WO3 structure. In accordance with catalyst activity tests and Raman spectroscopy, Ce2(WO4)3 was active site structure for OCM in the electric field. In-situ Raman spectroscopy revealed that Ce2(WO4)3/CeO2 structure was distorted and W-O bond weakened by application of the electric field. Consequently, it was suggested that the distorted W-O bond contributed to OCM activity in the electric field.

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