This is essentially a 2-stage reactor concept. In the case of a methanation reactor, a significant portion of the methanation is converted in a high-temperature, 1st stage reactor. A relatively high operating temperature can be utilized to maximize conversion. The 2nd reactor, or portion of the reactor, includes a temperature differential section which offers benefits as described above. Ideally, the process gas has already reached equilibrium conditions upon entry into the 2nd stage differential section. This will minimize reactor hardware and make the entire reactor scheme significantly more efficient. Experimental testing for this 2-stage concept is currently underway.