The present invention relates unique pore structures in nickel supported on alumina with the negligible formation of macropores. Incorporation of additional elements stabilizes the pore structure of the nickel supported on alumina. Additional element(s) were then further added into the nickel-supported materials. These additional element(s) further stabilize the pore structures under heating conditions. The improvements of pore structure stability under heating conditions and negligible presence of macropores limit the sintering of nickel metal to a mechanism of impeded diffusion. The negligible presence of macropores also limits the deposition of alkali metal hydroxide(s)/carbonate(s) on the outer shell of the catalyst pellet in the molten carbonate fuel cells. Both the negligible presence of macropores and improvement in pore structure stability allow for prolonging the catalyst life of these nickel supported on alumina catalysts of the present invention for reforming hydrocarbons.