Promotional effect of Mg on Fe catalyst during CO2 methanation

This study investigates CO 2 hydrogenation to CH 4 on a Mg-promoted Fe 2 O 3 catalyst, which reveals significant methanation activity. The influence of Mg on the textural and structural properties of fresh, H 2 -activated and spent catalysts was comprehensively examined using temperature-programmed reduction by H 2 , temperature-programmed desorption of NH 3 , CO 2 and H 2 , X-ray photoelectron spectroscopy, N 2 physisorption, in-situ Raman spectroscopy as well as ex-situ and in-situ X-ray diffraction. Carbonaceous species formed during CO 2 hydrogenation were characterized by temperature-programmed hydrogenation. The mechanistic results show that Mg retards iron oxide reduction during H 2 activation leading to the formation of smaller Fe crystallites compared to the unpromoted catalyst. Moreover, Mg enhances CO 2 and H 2 adsorption and increases the relative abundance of surface and bulk iron carbides thereby promoting CH 4 formation. The Mg promoter also controls carburization stabilizing the catalytically active Fe 3 C phase, while suppressing the formation of the carbon-rich and less active Fe 5 C 2 phase. However, Mg simultaneously also facilitates the deposition of unreactive carbon species.