Particle size is an important parameter of supported catalysts, but understanding the size-performance relationship is a challenge, especially in some complicated process. In this contribution, the particle size effect on CO2 hydrogenation to hydrocarbons over iron-based catalysts was deconvoluted into the effects on primary and secondary reactions. With a particle size range of 2.5-12.9 nm, the overall selectivity of C2+ hydrocarbons increases continuously, while that of CO decreases with the increasing size. The reverse water gas shift (RWGS) reaction and methanation are the main primary reactions and they are more sensitive within a particle size range of 6.1-12.9 nm. The formation of formate species is more favored, and thereby more CH4 is produced as a primary product on larger particles. The secondary process, the further hydrogenation of primary CO to hydrocarbons, is more sensitive within the particle size range of 2.5-9.8 nm, where the geometric effect or ensemble effect on larger particles leads to a higher chain-growth probability. More terrace sites may be conducive for C-C coupling, and the enhanced CO adsorption also benefits the secondary process. These findings highlight the deconvoluted particle size effect on CO2 hydrogenation and provide a dimension for understanding the catalysts in complicated reaction networks.
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