TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Reactor: The reactor has internal volume (V), comprising either an organized assembly of tubular form, based on the superposed layers of materials of similar chemical nature, in which the catalytic layer (CC1), capable of promoting the reaction of methanoxidation by gaseous oxygen to carbon monoxide, is located on the external surface of the assembly of tubular form closed at one of its ends, or a combination of several of these assemblies of tubular form that are mounted in parallel, and having free volume (Vf) inside the reactor greater than or equal to0.25V (preferably greater than or equal to0.5V).The reactor having a non-zero fraction of the volume (Vf) contains a steam-reforming catalyst.Preferred Components: The volume proportions of compounds (C12), (C34), (C56) and (C78) is 0 and the volume proportions of compounds (C2), (C4), (C6) and (C8) are 0.1-10%. (C1) Is La0.6Sr0.4Fe0.9Ga0.1O3-w, La0.8Sr0.2Fe0.7Ga0.3O3-w, La0.7Sr0.3Fe0.7Ga0.3O3-w or La0.5Sr0.5Fe0.9Ti0.1O3-w. (C3) Is La0.6Sr0.4Fe0.9Ga0.1O3-w, La0.9Sr0.1Fe0.9Ga0.3O3-w, La0.7Sr0.3Fe0.7Al0.3O3-w, La0.7Sr0.3Fe0.9Ga0.1O3-w, La0.8Sr0.2Fe0.7Ga0.3O3-w, La0.7Sr0.3Fe0.7Ga0.3O3-w, La0.5Sr0.5Fe0.9Ti0.1O3-w, La0.9Ti0.1Fe0.9Ti0.1O3-w, La0.6Sr0.4Fe0.2Fe0.1Co0.8O3-w, La0.7Sr0.3FeO3-w or La0.9Sr0.1Fe0.2Co0.8O3-w. (C5) Is La0.8Ce0.2Fe0.65Ni0.3Rh0.05O3-w, La0.8Ce0.2Fe0.7Ni0.3O3-w, La0.8Sr0.2Fe0.65Ni0.3Rh0.05O3-w, La0.6Sr0.4Fe0.7Ni0.3O3-w or La0.8Sr0.2Fe0.7Ni0.3O3-w. (C7) Is La0.6Sr0.4Fe0.9Ga0.1O3-w, La0.9Sr0.1Fe0.9Ga0.1O3-w, La0.7Sr0.3Fe0.7Al0.3O3-w, La0.7Sr0.3Fe0.9Ga0.1O3-w, La0.8Sr0.2Fe0.7Ga0.3O3-w, La0.7Sr0.3Fe0.7Ga0.3O3-w, La0.5Sr0.5Fe0.9Ti0.1O3-w, La0.9Sr0.1Fe0.9Ti0.1O3-w, La0.6Sr0.4Fe0.2Co0.8O3-w, La0.7Sr0.3FeO3-w or La0.9Sr0.1Fe0.2Co0.8O3-w.In the materials (AD1), (AP1), (AC1) and (AP2), the respective compounds (C2), (C4) and (C8) are selected from magnesium oxide, calcium oxide, aluminum oxide, zirconium oxide, titanium oxide, strontium-aluminum mixed oxides (SrAl2O4 or Sr3Al2O6), barium-titanium mixed oxide (BaTiO3), calcium-titanium mixed oxide (CaTiO3), La0.5Sr0.5Fe0.9Ti0.1O3-w or La06Sr0.4Fe0.9Ga0.1O3-w. Preferred Definitions:    Ma, Mc = La;    Ma1, Mc1 = Sr, Ba or Ca;    Ma2 = Al;    Mb = Fe, Ti or Ga;    Mc2 = Al, Ca or Ba;    Md = Fe;    Mf1 = Ni;    Mf2 = Rh;    Re1 = Sr;    Mf = Fe;    Mg = La;    Mg1 = Sr;    Mh = Fe;    Mg1 = Sr, Ba or Ca;    Mg2 = Al, Ba or Ca; and    x and v = 0.    EXAMPLE - A porous layer (CC1) was prepared by a conventional tape casting process using La0.8Ce0.2Fe0.7Ni0.3Od (where d is 3-delta). The pores in the layer after sintering were produced by the addition of a pore-forming agent to the liquid suspension of the ceramic material. A dense layer (CD1) was produced from a material (AD1) (containing La0.6Sr0.4Fe0.9Ga0.1Od (98 vol.%) and MgO (2 vol.%)) by a conventional tape casting process. A porous layer (CP1) was produced from a material (AP1) (containing La0.5Sr0.5Fe0.9Ti0.1Od (95 vol.%) and MgO (5 vol.%)) by tape casting process.    A multilayer perovskite catalytic membrane reactor (PCMR) of planar shape was produced by cutting tapes of CC1/CD1/CP1 layers. The stack then underwent bonding at pressure of 50 MPa and temperature above the glass transition temperatures of polymers used for the mechanical integrity of the tape (80degreesC). The multilayer obtained underwent a first heat treatment at 600degreesC with a slow temperature rise of 0.1-2degreesC/minute in air or nitrogen. The binder was removed and the multilayer was co-sintered at 1300degreesC for 30 minutes in nitrogen to obtain a multilayer (CC1/CD1/CP1) planar PCMR with a discrete porosity gradient in porous structure.