Bostan A. Oxidative Coupling of Methane over Perovskite Catalysts under Unsteady State Conditions.

The perovskite catalysts with АВО3 structure where А - Sr, Ba, La; B - Co, Mn, Ni and systems with partial substitution of А and В by alkali metals have been synthesized and investigated. It have been shown that Ni-соntaining perovskites are the most active catalysts of the OCM process, while Mn-соntaining samples have the lowest activity; Co-containing systems are the most stable catalysts. It has been determined that modification of perovskites with alkali metal cations leads to increase both specific catalytic activity and selectivity on С2-hydrocarbons, this may be connected with the increasing of oxygen deficiency (the concentration of oxygen vacancies) in perovskite structure. High selective and active catalysts for the OCM process, based on SrCoO3-x, have been worked out. The sample Sr0.75Na0.125K0.125CoО3 was stable in work (50 h), keeping high selectivity to С2+-hydrocarbons (> 90%) at 1023 K. The perovskite catalyst SrLi0.75Co0.25O3-x in temperature interval of 973-1048 К revealed 100% selectivity with respect to С2+-hydrocarbons. It has been shown that in periodic catalytic mode, when methane and oxygen react with oxide catalyst alternatively, the ОСМ process is more selective with respect to С2+-hydrocarbons, than in stationary one. It has been established, that reaction of С2-hydrocarbons and carbon dioxide are characterized the first and, accordingly, zero order on methane. According to ТАР method, the mechanism of OCM process in periodic mode has been proposed. The ways of increasing of efficiency of the OCM process in periodic mode have been proposed, which can be applied in pilot plants of methane direct conversion to higher hydrocarbons.