The role of Na for efficient CO2 hydrogenation to higher hydrocarbons over Fe-based catalysts under externally forced dynamic conditions

•A series of Fe-based catalysts differing in surface Na/Fe ratio were prepared.•The critical role of Na is beyond its promotional effects under stationary operation.•Surface Na/Fe ratio determines the response of performance to fluctuating conditions.•Catalyst dynamics induced by fluctuating reaction conditions were studied.•The effect of Na in securing iron carbides was studied by in situ characterization.