Oxidative Coupling of Methane over Mixed Metal Oxide Catalysts Consisting of Group 1 and Group 5 Metals.

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  • YAMAMURA Masami
    JAPEX Research Center, Japan Petroleum Exploration Co., Ltd.
  • OKADO Hideo
    JAPEX Research Center, Japan Petroleum Exploration Co., Ltd.
  • TSUZUKI Naohide
    JAPEX Research Center, Japan Petroleum Exploration Co., Ltd.
  • OTSUKA Kiyoshi
    Dept. of Chemical Engineering, Faculty of Engineering, Tokyo Institute of Technology

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Other Title
  • １族／５族系複合金属酸化物を触媒とするメタン酸化カップリング反応

Abstract

Binary catalysts were prepared by admixing alkali metals (group 1 metals: Li, Na, K) and group 5 metals (V, Nb, Ta) with group 1 to group 5 atomic ratios of 1:1 and 1:0.3, and their catalytic performance for oxidative coupling of methane as well as their physicochemical properties were investigated. The catalytic activity and selectivity to C2 and higher hydrocarbons (C2+) changed by varying either the combination of alkali and group 5 metals or the atomic ratio of the two group metals. The activity and selectivity were improved in the order: Li>Na>K for alkali metals and Ta>Nb>V for group 5 metals. Catalysts with the atomic ratio of 1:0.3 showed higher activity and C2+ selectivity than the catalysts with the atomic ratio of 1:1.<br>From X-ray diffraction analysis, it was found that the crystalline structures of the catalysts prepared with an atomic ratio of 1:1 were all ABO3 types, where group 1 and 5 metals are designated by A and B, respectively. On the other hand, when the amount of a group 5 metal was decreased to an atomic ratio of 1:0.3, lithium and sodium reacted with group 5 metals to produce complex metal oxides of A3BO4 type, whereas potassium did not produce this type of oxide with any group 5 metal. The A3BO4 type oxide catalysts gave higher C2+ selectivity than the ABO3 type. The thermal analysis of catalysts left in air for a long period of time showed that A3BO4 type oxides had basic sites which could adsorb carbon dioxide and desorb it at >700K, but that ABO3 type oxides had no such basic site. This seems to explaine the fact that A3BO4 type catalysts give higher C2+selectivity in oxidative coupling of methane.

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