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CO 2 hydrogenation on a K-promoted Fe catalyst was studied in a fixed-bed microreactor between 300 and 400 °C, at 1 MPa, and with modified residence times in the range of 0.042-21.4 g‚s/ cm 3 . For temperatures below 360 °C, organic products almost identical with those found in the traditional Fischer-Tropsch reaction with H 2 /CO were found (paraffins and R-olefins). At 400 °C, formation of carbon deposited on the catalyst became a major reaction. Concerning the mechanism of hydrocarbon formation, the effect of residence time resulted in catalyst particle selectivity values for hydrocarbons always higher than zero. This indicates that, besides the two-step reaction mechanism via CO, a direct hydrocarbon formation from CO 2 can occur in principle. With a reaction scheme proposed from these experimental results, a kinetic model was developed using integration and regression features of ASPEN PLUS. Calculated values for CO 2 conversion and CO and total hydrocarbon selectivities agree with the experimental data within a range of error less than 15%.

Impregnated and co-precipitated, promoted and unpromoted, bulk and supported iron catalysts were prepared, characterized, and subjected to hydrogenation of CO 2 at various pressures (1-2 MPa) and temperatures (573-673 K). Potassium, as an important promoter, enhanced the CO 2 uptake and selectivity towards olefins and long-chain hydrocarbons. Al 2 O 3 , when added as a structural promoter during co-precipitation, increased CO 2 conversion as well as selectivity to C 2? hydrocarbons.

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