Active site for syngas production by direct partial oxidation of CH over ZrO

• Published in: Catalysis science & technology Vol. 14; no. 11; pp. 3253 - 3264
• Main Authors: Murata, Kazumasa, Arai, Keita, Kondo, Nao, Manabe, Ryo, Yumura, Takashi, Hosokawa, Saburo
• Format: Journal Article
• Published: 04.06.2024
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/d4cy00187g

The production of high-value-added chemicals and their raw materials by partial oxidation of methane (POM) is advantageous. The screening of 31 simple oxide catalysts for direct POM showed that ZrO 2 had the highest syngas yield (CO and H 2 ) and was thus a promising catalyst. Kinetic analysis indicated that POM over the ZrO 2 catalyst proceeded in a Langmuir-Hinshelwood mechanism and that CH 4 activation was the rate-limiting step. Density functional theory calculations showed that CH 4 was activated on coordinatively unsaturated Zr 4+ cations formed by the dehydration of the hydroxyl groups on the ZrO 2 surface. In situ diffuse reflectance infrared Fourier transform spectroscopy revealed that CH 4 was converted into CO and H 2 through CH 4 -oxygenated intermediates, such as methoxy and formate species. The CH 4 -oxygenated intermediates on the ZrO 2 catalyst were closely related to the catalytic performance of the oxide catalysts in POM. A comprehensive investigation of the POM reaction over ZrO 2 -based catalysts was then conducted. ZrO 2 modification with tungsten oxide (WO x ) or lanthanum oxide (LaO x ) was examined to determine their ability to improve the catalytic properties of ZrO 2 for POM. ZrO 2 modification with WO x and LaO x enhanced its acidity and basicity, respectively. CO selectivity was increased by modifying ZrO 2 with a small amount of WO x . Moreover, modification with LaO x increased CH 4 conversion and H 2 yield at low temperatures. ZrO 2 is a promising catalyst for direct partial oxidation of methane. The reaction mechanism and active site for partial oxidation of methane over ZrO 2 were proposed using kinetic analysis, in situ diffuse reflectance infrared Fourier transform spectroscopy, and DFT calculations.