Controlled-pore catalyst structures and process for producing synthesis gas

Controlled pore structure catalysts are disclosed that are active for catalyzing the partial oxidation of methane to CO and H 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° 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.