New results studying the effects brought about by the introduction of small amounts of N2O in the gas feed (promoter) during the partial oxidation of methane (POM) over Rh/gamma-Al2O3 and Rh/MgO catalysts are presented. Standard tests were performed with 5 vol.% CH4, 2.5 vol.% O-2, and balanced with N-2. When small amounts of N2O (300 ppm, 1000 ppm) were added to the feed, yield and selectivity to H-2 and CO increased. Under these conditions rhodium works in a reduced state, resulting in the enhancement of syngas selectivity and the inhibition of the total oxidation of methane. This effect tends to disappear after a certain period of time when N2O supply is cut. The effect is reversible. It is suggested that N2O is adsorbed on the vacancies where O-2 does, inhibiting the formation of oxidant (electrophilic) oxygen species produced by dissociation of O-2 on the same vacancies. In the presence of N2O, rhodium remains in a reduced oxidation state. Reduced rhodium modifies the kinetics of all reactions involved under POM reaction conditions and promotes synthesis gas. (C) 2012 Elsevier B. V. All rights reserved.