A process for adiabatically prereforming a feedstock, includes: providing an adiabatic reactor; providing a catalyst containing 1-20 wt. % nickel and 0.4-5 wt. % potassium, wherein the catalyst has an overall catalyst porosity of 25-50% with 20-80% of the overall catalyst porosity contributed by pores having pore diameters of at least 500 .ANG.; providing the feedstock containing natural gas and steam, wherein the natural gas contains an initial concentration of higher hydrocarbons, and a ratio of steam to natural gas in the feedstock is from 1.5:1 to 5:1; preheating the feedstock to a temperature of 300-700.degree. C. to provide a heated feedstock; providing the heated feedstock to the reactor; and producing a product containing hydrogen, carbon monoxide, carbon dioxide, unreacted methane, and steam, wherein said product contains a reduced concentration of higher hydrocarbons less than the initial concentration of higher hydrocarbons, to prereform the feedstock.