To produce nitrogen-free synthesis gas or hydrogen by the partial oxidation of methane using air as an oxidant, NiO-Cr 2 O 3 -MgO complex oxide was proposed as an effective one. Lattice oxygen of NiO in the complex oxide was effectively transferred to CH 4 to give H 2 and CO in the ratio of 2-3:1 at 700 °C. NiO was reduced to metallic Ni during the course of the reaction with CH 4 , and the reduced Ni was successfully oxidized to NiO with air at 700 °C. Repeated cycles of the reaction and oxidation were carried out without any loss of activity. The role of Cr 2 O 3 seemed to weaken the Ni-O bond in NiO-MgO complex oxide, in which NiO is less reducible with CH 4 at 700 °C. In addition, the surface oxidation state of Ni was increased to Ni 3+ with Cr 2 O 3 .

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In order to generate synthesis gas or hydrogen free from nitrogen by partial oxidation of methane using air as an oxidant, gas-solid reactions of methane and a metal oxide and/ or mixed metal oxides were carried out. The background of the gas-solid reaction was briefly reviewed and then a series of the present author's studies was described. As metal oxides Fe 2 O 3 and NiO were active, but the reaction with methane and these oxides afforded complete oxidation to give H 2 O and CO 2 . To both oxides, addition of Cr-and Mg-oxides promoted the following reaction to give synthesis gas.After the reaction with methane, mixed oxides were reduced to lower valence state oxides and they were regenerated by the oxidation with air.

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