Porous cryptomelane-type octahedral molecular sieve manganese oxide (K-OMS-2) supported iron nanocatalysts have been developed for selective hydrogenation of CO2 and CO to light olefins. Surface coated iron (SCI) catalysts and frame-work doped iron (FDI) catalysts have different interfaces. The synergistic interactions of nano-size iron carbides, potassium promoters, and manganese oxides vary in these two types of the Fischer-Tropsch (F-T) catalysts with respect to their catalytic activities and selectivity. For example, the SCI catalysts have high selectivity (>95%) to light olefins but low catalytic activity with a CO conversion of 45% and a CO2 conversion of 32%. The FDI catalysts showed higher catalytic activities with a CO conversion of 87% and a CO2 conversion of 45%. Direct analyses in real time-mass spectra and temperature programmed reduction-mass spectra have been used to correlate temperature effects. These component-structure-activity relationships provide insight for CO2 utilization and F-T syntheses. (c) 2012 Elsevier B.V. All rights reserved.