Oxidative coupling of methane over unsupported and alumina-supported samaria catalysts

Authors:  Trenton W. Elkins, Helena E. Hagelin-Weaver

Abstract:
Being the shortest unsaturated hydrocarbon, ethylene is a valuable feedstock gas for synthesizing longer chain hydrocarbon products. Using the oxidative coupling of methane to produce ethylene and ethane (C₂ products) has been studied extensively over the past few decades. In this work, samaria nanoparticles (NPs) and alumina-supported samaria catalysts were prepared using different methods (water/toluene reverse microemulsion, metal-oleate high temperature decomposition, and incipient-wetness impregnation followed by calcination) and various types of alumina supports (high and low surface area nanoparticle alumina [n-Al₂O₃(+), n-Al₂O₃(−)] and a porous gamma alumina support [p-Al₂O₃]). The highest product yields were obtained over Sm₂O₃ NPs synthesized using the metal-oleate high temperature decomposition and a nitrate precursor. Using a chloride precursor in the preparation of the Sm₂O₃ NPs resulted in less active and selective catalysts, and should be avoided. While the C₂ selectivities were lower over the Sm₂O₃/Al₂O₃ catalysts, the yield per gram of Sm₂O₃ were higher compared with the Sm2O3 NPs. The best supported catalyst was the Sm₂O₃/n-Al₂O₃(−) prepared using incipient wetness impregnation of a nitrate precursor, since this leads to the smallest Sm₂O₃ particles as well as the largest coverage of the acidic Al₂O₃ support. XRD analysis revealed that high-temperature calcinations form SmAlO3 on the Al2O3-supported catalysts. While this reduced the near surface Sm₂O₃ concentration, it had beneficial effects as it also lowered the Al₂O₃ content. Therefore, Al2O3-supported Sm₂O₃ warrants further investigation, as surface modifications of the Al₂O₃ can reduce its acidity and lead to higher C₂ selectivities in the oxidative coupling of methane over these catalysts.

Keywords:
Samarium oxide nanoparticles
Alumina-supported samaria
Methane coupling activity and selectivity
XRD
XPS

Published in: Applied catalysis A: General  (Volume 454, Pages 1-172, 15 March 2013)

Publisher: Elsevier

ISSN Information: 0926-860X

Oxidative coupling of methane over unsupported and alumina-supported samaria catalysts

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