A catalyst for adiabatically prereforming a feedstock wherein the catalyst comprises 1 to 20 wt. % nickel and 0.4 to 5 wt. % potassium on a calcium aluminate support. The overall catalyst porosity is greater than 40% with greater than 70% of the overall catalyst porosity contributed by pores having pore diameters of at least 500 .ANG., and having a median pore diameter greater than 2600 .ANG., and having a nitrogen BET area less than 6.5 m.sup.2/g.