Abstract
Involvement of lattice oxygen in the oxidative coupling of methane over MgO, Li-MgO, Mn-MgO, Li-Mn-MgO, Cd-MgO, Li-Cd-MgO, Zn-MgO and Li-Zn-MgO catalysts at 1073 K has been investigated by carrying out the reaction in the absence of free oxygen as a function of methane pulse number, using a pulse microreactor connected to a gas chromatograph. The influence was also studied of catalyst reoxidation after the pulse experiments on the conversion of methane and C 2-selectivity in the pulse reaction. A high C 2 selectivity in the methane pulse reaction is observed for the lithium-promoted catalysts. The order of the C 2 selectivity observed on the catalysts with and without the lithium promoter was found to be as follows: Li-Zn-MgO > Li-Cd-MgO > Li-Mn-MgO ≃Li-MgO⩾ Cd-MgO≫ Zn-MgO > Mn-MgO > MgO. Upon reoxidation of the reduced catalyst in pulse experiments, the selectivities in the formation of carbon monoxide, carbon dioxide and C 2 hydrocarbons are strongly influenced, due to the formation of active chemisorbed oxygen species and/or restructuring of the catalyst surface.
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