Methanation of CO2 using Mg-modified Fe catalysts

The hydrogenation of CO 2 to CH 4 was studied over a series of Mg-promoted Fe catalysts containing 2 wt% Mg. The catalysts were synthesized using different preparation methods and Mg precursors to systematically assess the impact of bulk and surface properties on catalytic behavior. Comprehensive characterization was performed using X-ray diffraction, N 2 physisorption, 57 Fe Moessbauer spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction by H 2 , temperature-programmed desorption of NH 3 and temperature-programmed hydrogenation. Structure–activity relations indicate that a homogeneous Mg distribution in the bulk enhances the formation of surface defects and amorphous phases, while improving the reducibility of the fresh catalysts. These characteristics promote the formation of iron carbide and carbonaceous surface species, which are identified as the active phases responsible for CH 4 formation during CO 2 hydrogenation. The reverse water–gas shift reaction was found to be a key step driving CO 2 activation. The catalyst prepared by flame spray pyrolysis using magnesium acetate as precursor exhibited the highest performance. Under industrially relevant conditions (400 °C, 14 bar, 8500 h⁻ 1 ), a CO 2 conversion of 68% and a CH 4 selectivity of 78% were achieved, representing the highest efficiency reported to date for Fe-based catalysts.