Controlled pore structure catalysts are disclosed that are active for catalyzing the partial oxidation of methane to CO and H.sub.2 and, advantageously, are capable of initiating the reaction without the need for an additional ignition source. A preferred catalyst comprises rhodium and samarium supported on an alumina or modified alumina support having certain surface area, pore volume, pore size and metal dispersion characteristics that permit light-off of the reaction at temperatures below 500.degree. C. and with little or no use of an ignition agent. A method of partially oxidizing a light hydrocarbon to form synthesis gas, and a method of enhancing low-temperature light-off of the process are also described.