Thermodynamic Analysis of CO2 Hydrogenation to Higher Alcohols (C2-4OH): Effects of Isomers and Methane

NiFe and CoFe nanocatalysts supported on highly dispersed alumina-silica: Structure, surface properties, and performance in CO2 methanation

The hydrogenation of CO2 to CH4 has gained considerable interest in terms of sustainable energy and environmental mitigation. In this regard, the present work aims to investigate the adsorptive concentration and CO2 methanation performance over CoFe and NiFe bimetallic catalysts supported on fumed alumina-silica SA96 support at 170-450 °C and under atmospheric pressure. The catalysts were prepared by wet impregnation method, subjected to calcination and further reduced with hydrogen, and their performance in CO2 methanation was investigated in a hydrogen-rich 2%CO2-55%H2-43%He gas mixture. In this study, we describe the crystal and mesoporous structures of the prepared catalysts by in-situ XRD and ex-situ nitrogen adsorption, evaluate the NiFe and CoFe metal surface states before and after catalysis by XPS, visualize the surface morphology by SEM, estimate the catalytic activity by gas chromatography, and investigate the adsorbed surface species, showing the presence of *HCOO/*HCO and *CO intermediates, determine two possible pathways of CH4 formation on the studied catalysts by temperature-programmed desorption mass spectrometry, and correlate the structural and surface properties with high CO2 conversions up to 100% and methanation selectivities up to 72%. The latter is related to changes in the elemental chemical states and surface composition of CoFe and NiFe nanocatalysts induced by treatment under reaction conditions, and the surface reconstruction during catalysis transfers the part of active 3d transition metals into the pores of the SA96 support. Our thorough characterization study with complementary techniques allowed us to conclude that this high activity is related to the formation of catalytically active Ni/Ni3Fe and Co/CoFeOx nanoscale crystallites under H2 reduction and their maintenance under CO2 methanation conditions. The successfully applied combination of CO2 chemisorption and thermodesorption techniques demonstrates the ability to adsorb the CO2 molecules by supported NiFe and CoFe nanocatalysts and the pure alumina-silica SA96 support.

Recent Advances Hydrogenation of Carbon Dioxide to Light Olefins over Iron-Based Catalysts via the Fischer-Tropsch Synthesis

The massive burning of fossil fuels has been important for economic and social development, but the increase in the CO2 concentration has seriously affected environmental sustainability. In industrial and agricultural production, light olefins are one of the most important feedstocks. Therefore, the preparation of light olefins by CO2 hydrogenation has been intensively studied, especially for the development of efficient catalysts and for the application in industrial production. Fe-based catalysts are widely used in Fischer-Tropsch synthesis due to their high stability and activity, and they also exhibit excellent catalytic CO2 hydrogenation to light olefins. This paper systematically summarizes and analyzes the reaction mechanism of Fe-based catalysts, alkali and transition metal modifications, interactions between active sites and carriers, the synthesis process, and the effect of the byproduct H2O on catalyst performance. Meanwhile, the challenges to the development of CO2 hydrogenation for light olefin synthesis are presented, and future development opportunities are envisioned.