Fe based core–shell model catalysts for the reaction of CO2 with H2

Abstract

Fe@SiO2 core–shell model catalysts were investigated for the conversion of CO2 and H2 into CH4, CO and H2O. For evaluation of the effect of core size on the catalytic activity, samples with Fe particle sizes of 4, 6 and 8 nm were prepared. Fresh and spent catalysts were thoroughly characterized by X-ray diffraction, 57Fe Mössbauer spectroscopy, transmission electron microscopy, temperature programmed hydrogenation and X-ray photoelectron spectroscopy. As a result, the yield of the major product CO as well as CH4 was increased with Fe core size. Additionally, growing Fe cores led to stronger carburization and higher amount of reactive carbide entities, which drive the CH4 formation. Finally, formation of inactive bulk carbon deposition is strongly suppressed for the core–shell catalysts in comparison to bulk iron oxide catalysts used for CO2 hydrogenation.

Iron Based Core-Shell Structures as Versatile Materials: Magnetic Support and Solid Catalyst

“…26° 2θ identified as amorphous SiO2 from the particle shell. Though Fe3O4 has similar crystalline structures and lattice parameters, this phase is excluded by previous 57 Fe Mössbauer experiments for similar synthesized coreshell material [7].…”

“…Therefore, α-Fe 2 O 3 reflexes are not considered for further evaluation and discussion. The major phase in the core-shell materials is represented by nanoscale γ-Fe 2 O 3 with the most pronounced reflexes at the lattice planes defining Miller indices (hkl) of hkl = (022), (311), and (511), according to the literature [7,18]. All respective PXRD patterns show a broad reflex at ca.…”

“…The obtained result and 60 kJ/mol fit well with literature values in the order of 50 kJ/mol [23] for both ca tested, respectively. The selectivity toward CO increases significantly from 75% to 9 15Fe(4)@SiO2 and from 91% to 98% for 13Fe (8) This issue is stated to be highly dependent on particle size and, thus, is still a m current research [7]. Though the value of the activation energy might be affected dynamic change of the catalyst under reaction conditions, the order of magnitud cates the absence of severe mass transport limitations through the SiO2 shell.…”

“…The selectivity toward CO increases significantly from 75% to 98% for 15Fe(4)@SiO 2 and from 91% to 98% for 13Fe(8)@SiO 2 between 350 and 390 • C. It has to be mentioned, though, that no stable catalyst activity is achieved after 12 h TOS, due to dynamic restructuring and Fe carbide formation (see Supplementary Materials, Figure S4). This issue is stated to be highly dependent on particle size and, thus, is still a matter of current research [7]. Though the value of the activation energy might be affected by the dynamic change of the catalyst under reaction conditions, the order of magnitude indicates the absence of severe mass transport limitations through the SiO 2 shell.…”

“…In catalytic processes, such as the power-to-methane process, it is considered a promising replacement for nickel and cobalt as active materials, as it provides high selectivity in the methanation 2 of 16 step [6] and flexibility toward various mixtures of H 2 /CO/CO 2 . The limited reactivity and the formation of different carbonaceous species under reaction conditions, however, is still a challenge, which is a matter of ongoing research [7,8]. For this purpose, the welldefined structure of Fe-based core-shell materials is highly promising in order to derive structure-activity relationships as the basis for design of stable, active, and selective catalysts.…”