Oxidative Coupling of Methane over Samarium Oxide Doped with Alkali Fluorides.

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  • アルカリフッ化物担持酸化サマリウム触媒によるメタンの酸化カップリング

Abstract

Since samarium oxide has been reported as a catalyst capable of high methane conversion for oxidative coupling of methane, samarium oxides modified by doping with lithium-, sodium-, and potassium-fluorides were prepared for improving the selectivities for ethylene and ethane (referred to as C2-selectivity) and catalytic durability. The samarium oxides modified by doping with any alkali fluoride showed high C2-selectivity. The oxides modified with lithium fluoride gave high methane conversion and C2-selectivity especially, giving the highest yield of ethylene and ethane (referred to as C2-yield) of 27.8%, which was greater than that being considered as a limiting C2-yield (<25%) for oxidative coupling of methane.<br>The catalytic activity of the modified samarium oxides with lithium fluoride prepared by the impregnation method decreased after 80h of reaction. The deactivation was due to the vaporization of lithium fluoride from the catalyst surface and to the transformation of the crystal structure of samarium oxide from cubic to monoclinic. On the other hand, the modified catalyst prepared by sol-gel method showed a high catalytic durability capable of maintaining a high C2-yield (>21.6%) for more than 500h on stream. The lithium fluoride highly dispersed in the bulk of this catalyst must have diffused to the surface to make up for the lost lithium fluoride therefrom during reaction.

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