Spatially resolved analysis of CO2 hydrogenation to higher hydrocarbons over alkali-metal promoted well-defined FexOyCz.

[Display omitted] • Well-defined Fe x O y C z compositions promoted with Li, Na, K, Rb or Cs were prepared. • They were tested in CO 2 hydrogenation to higher hydrocarbons. • Stationary phases and their spatial distribution depend on alkali metal type. • Steady-state Fe 5 C 2 /Fe 3 C ratio determines the selectivity to C 2+ -hydrocarbons. • The kind of alkali metal affects reaction pathways of CH 4 formation. A series of catalysts for CO 2 hydrogenation to higher (C 2+) hydrocarbons were prepared through controlled decomposition of iron (II) oxalate dihydrate impregnated with Li, Na, K, Rb or Cs carbonate. They consist of Fe 3 O 4 , Fe 5 C 2 , Fe 3 C and Fe. Their steady-state spatial phase distribution is, however, affected by the presence and the kind of the promoter. These structural characteristics determine catalyst activity and product selectivity. Fe 3 C seems to favor CH 4 formation, while C 2+ -hydrocarbons are formed over Fe 5 C 2. A positive relationship between the rate of C 2+ -hydrocarbons formation and the rate constant of dissociation of adsorbed CO 2 was established, while an opposite dependence is valid for the rate of CO 2 methanation. The rate constant of this reaction increases in the presence of alkali metal and with an increase in its atomic number. Therefore, CH 4 is mainly formed over Rb- or Cs-doped catalysts through CO hydrogenation, while CO 2 methanation prevails over the remaining catalysts. [ABSTRACT FROM AUTHOR]