Abstract The activities are reported of reduced precipitated iron catalysts and promoted and unpromoted iron synthetic ammonia catalysts for benzene hydrogenation over the temperature range 380–473 K. Singly promoted iron (5.50% Al2O3) was the most active of the iron catalysts, being, at 450 K, some 22 times more active than unpromoted iron and some 4.5 times more active than iron prepared by NaOH precipitation of the hydroxide. The results with doubly promoted iron (2.29% Al2O3, 1.64% K2O) were somewhat equivocal in that benzene was more strongly absorbed on this catalyst and cracking was more extensive at all temperatures. Both iron nitride, Fe4N, and iron carbide, Fe2C, prepared by nitriding and carbiding reduced unpromoted iron showed no benzene hydrogenation activity. A reduced copper catalyst had, effectively, zero activity under these reaction conditions (~7:1 H2:C6H6). However, a reduced nickel catalyst was more than 4 times more active than singly promoted iron at 450 K and was able to maintain this higher activity for long contact periods. All of the iron catalysts showed a (frequently sharp) decrease in activity with time attributed to adsorption of hydrocarbon complexes which can under certain conditions lead to the formation of nuclei of an iron carbide.