TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The metal catalyst is selected from supported metal clusters (preferably comprising at least one metal of Groups 4, 5 and/or 6 of the Periodic Table of the Elements, especially tantalum). The metal catalyst is selected from metal hydrides, organometallic compounds and organometallic hydrides, supported on and preferably grafted onto a solid support. The metal catalyst comprises at least one metal selected from lanthanides, actinides and metals of Groups 2 to 12 (preferably from transition metals of Groups 3 to 12, especially of Groups 3 to 10) of the Periodic Table of the Elements. The metal catalyst selected from organometallic compounds and organometallic hydrides comprises at least one hydrocarbon radical (R), either optionally saturated, linear or branched (preferably 1-20C, especially 1-14C hydrocarbon). The solid support is selected from metal oxides, metal sulfides, metal carbides, metal nitrides, metal salts, refractory oxides, refractory sulfides, refractory carbides, refractory nitrides and refractory salts, and from carbon, mesoporous materials, organic or inorganic hybrid materials, metals and molecular sieves. The selective hydrogen-permeable membrane is selected from microporous inorganic membranes and dense inorganic membranes, preferably supported on a porous inorganic support particularly selected from porous metallic supports, porous steel supports, porous ceramic supports, porous glass supports and porous refractory oxide supports. The microporous inorganic membrane is selected from microporous silica membranes, microporous alumina membranes, microporous zirconia membranes, microporous aluminum-doped silica membranes, microporous binary alumina-silica membranes, microporous binary zirconia silica and microporous binary zirconia-alumina membranes. The microporous inorganic membrane is selected from zeolite membranes (preferably from polycrystalline zeolite membranes). The dense inorganic membrane is selected from dense metallic membranes, dense ceramic membranes and dense cermet (ceramic-metal) membranes, preferably supported on a porous inorganic supports particularly selected from porous metallic supports, porous steel supports, porous ceramic supports, porous glass supports and porous refractory oxide supports. The dense metallic membrane comprises at least one metal selected from Groups 4 to 11 (preferably Groups 4 to 6 and Groups 8 to 11, especially Groups 8 to 11, particularly Group 10) of the Periodic Table of the Elements. The dense metallic membrane comprises at least one metal selected from nickel, palladium and platinum, preferably palladium or palladium alloy, especially comprising palladium and at least one other metal selected from cerium, yttrium, ruthenium, osmium, nickel, platinum, copper, silver and gold, especially silver. The dense metallic membrane is a palladium and/or palladium alloy membrane, preferably a palladium and/or palladium-silver alloy membrane, particularly supported on a porous metallic or ceramic support. The dense ceramic membrane is selected from proton conducting ceramic membranes, preferably from perovskite type proton-conducting ceramic membranes. The proton-conducting ceramic membrane is based on the formula AB'(1-x)(B1a)xO3.A=calcium, strontium or barium atom, preferably a strontium or barium atom;B'=an atom of cerium;B1a=titanium, vanadium, chromium, manganese, iron, copper, yttrium, praseodymium, terbium, thulium or ytterbium atom, preferably a thulium atom;x=0 to 0.2 (preferably 0-0.1).    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Reactor: The membrane reactor is equipped with the selective hydrogen-permeable membrane comprising a reaction side facing the metal catalyst and the reaction mixture present in the interior of the membrane reactor under an absolute total pressure (P'), and a permeate side facing the exterior of the membrane reactor submitted to an external absolute pressure (P'') lower than the pressure (P'), so that it results in a pressure difference through the membrane selected from 0.05 to 5 MPa (preferably 0.1 to 2 MPa, especially 0.2 to 1 MPa). The permeate side of the membrane is subjected to a sweep gas flow preferably selected from inert gases, particularly from nitrogen, argon and helium, in particular so as to entrain the hydrogen externally to the membrane and to form a permeate gas mixture comprising the hydrogen and the sweep gas. The membrane reactor is selected from sweep-flow membrane reactors.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The methane is used alone or in the form of a mixture of methane with less than or equal to 1 mole% of at least one other alkane (preferably selected from +2C alkanes having greater than or equal to 2C (preferably is used in the form of a mixture of methane with at least one other alkane preferably selected from +2C alkanes having greater than or equal to 2C), where the methane is in a molar proportion higher than 50-lower than 99% (preferably higher than 60-lower than 99%, especially higher than 75%-lower than 99%). The methane is used in the form of natural gas. Preferred Method: The contacting is performed at a temperature selected from 150-700 (preferably 200-650, especially 250-600, particularly 300-600) degrees C. The contacting is performed under an absolute total pressure (P') selected from 0.1 to 50 MPa (preferably 0.1-30 MPa, especially 0.1-20 MPa). The contacting involves adding the methane to the metal catalyst, or adding the metal catalyst to the methane, or adding the methane and the metal catalyst simultaneously into the reaction zone, preferably continuously. EXAMPLE - A control method for conversion of methane into ethane by a non-oxidative methane coupling reaction was carried out in a standard gas phase reactor comprising no selective hydrogen-permeable membrane, in the following manner: methane at a continuous flow rate, R', of 3 ml/minutes and under a total absolute pressure, P', of 5 MPa was continuously introduced into and passed through a gas phase dynamic reactor previously heated to 350 degrees C and containing 0.5 g of the metal catalyst (C1) comprising tungsten grafted onto alumina support, mixed and diluted with 8 g of the gamma -alumina. Contacting the methane with the metal catalyst (C1) continuously during a time of 8000 minutes under these conditions resulted in the production of ethane with a selectivity by weight for ethane with respect to carbon-containing products produced which was greater than 99.9%. In particular, no detectable traces of alkenes or alkynes, such as ethylene or acetylene, or aromatic compounds, such as benzene, or carbon monoxide, or carbon dioxide were found. Methane was continuously converted during 8000 minutes expressing the percentage of methane conversion (C%) versus time (T) in minutes. Curve (1) showed initial conversion percentage (C%) of 0.02% (after 550 minutes) and a final conversion percentage (C%) of 0.12% (after 8000 minutes). A test method for conversion of methane into ethane was carried out in a membrane reactor by a non-oxidative methane coupling reaction in a similar manner as the control, apart from the fact that a gas phase dynamic sweep-flow membrane reactor comprising a selective hydrogen-permeable membrane was used instead of the standard gas phase dynamic reactor. The selective hydrogen-permeable membrane was a dense metallic membrane supported on a porous metallic support, especially a palladium/silver (75/25 by weight) alloy layer coated by a palladium film and supported on a chromium-nickel alloy support. The membrane arranged in the membrane reactor comprised a reaction side and a permeate side. The reaction side of the membrane was facing the metal catalyst (C1) and the reaction mixture produced in the membrane reactor i.e. the interior of the membrane reactor, where methane was continuously introduced and contacted with the metal catalyst (C1) under an absolute total pressure (P'). The permeate side of the membrane was facing the exterior of the membrane reactor and was submitted to an external absolute pressure, P'', so that it resulted in a pressure difference through the membrane. The permeate side of the membrane was also subjected to a sweep gas flow consisting of argon under the external absolute pressure (P'') and flowing at a continuous flow rate (R''), so as to form a permeate gas mixture comprising the argon and the hydrogen having permeated the membrane. Thus, methane at a continuous flow rate (R') of 3 ml/minutes and under a total absolute pressure (P') of 5 MPa was continuously introduced into and passed through the membrane reactor previously heated to 350 degrees C and containing 0.5 g of the metal catalyst (C1), mixed and diluted with 8 g of gamma -alumina. The external absolute pressure (P'') was continuously maintained at 4.5 MPa, so that the pressure difference through the membrane was equal to 0.5 MPa, and the argon used as a sweep gas was continuously flowing at a continuous flow rate (R'') of 3 ml/minutes under the pressure (P'') and at a temperature of 350 degrees C. Contacting the methane with the metal catalyst (C1) continuously during a time of 8000 minutes under these conditions resulted in the production of ethane with a selectivity by weight for ethane with respect to carbon-containing products produced which was very high and greater than 99.9%. No detectable traces of alkenes or alkynes, such as ethylene or acetylene, or aromatic compounds, such as benzene, or carbon monoxide, or carbon dioxide were found. Methane was continuously converted during a time of 8000 minutes according to a Curve expressing the percentage of methane conversion (C%) versus time (T) in minutes. Curve (2) showed initial conversion percentage (C%) of 0.45% (after 500 minutes) and a final conversion percentage (C%) of 0.25% (after 8000 minutes). The use of a membrane reactor was able to accelerate the catalyst activation time from about 3000 minutes in a standard case to less than 500 minutes, and to provide an extremely high maximum catalyst activity during the initial reaction phase and finally a global methane conversion maintained at a very high level, compared to those obtained in a control.