Iron–Potassium on Single-Walled Carbon Nanotubes as Efficient Catalyst for CO₂ Hydrogenation to Heavy Olefins

The iron–potassium catalysts supported on single- and multiwalled carbon nanotubes, FeK/SWNTs and FeK/MWNTs, were fabricated, characterized, and evaluated in CO₂ hydrogenation. The FeK/SWNTs catalyst outperforms the FeK/MWNTs catalyst in selectivity during CO₂ hydrogenation to olefins with the selectivities being 62.3% and 52.4%, respectively. Of particular interest is that the FeK/SWNTs catalyst is more selective toward heavy olefins (C₅₊⁼ selectivity, 39.8%), whereas the FeK/MWNTs catalyst is more selective to light olefins (C₂–C₄⁼ selectivity, 30.7%). The FeK/SWNTs catalyst also affords much lower selectivities to undesired CO and CH₄ in addition to higher productivity of hydrocarbons, thus resulting in an unprecedentedly high productivity of heavy olefins of 27.6 μmol_CO2 g_Fe^–1 s^–1. The more electron-enriched exterior of SWNTs with large curvature, higher abundance of Hägg carbide, and stronger interaction with light olefins may rationalize the superior catalytic behavior of the FeK/SWNTs catalyst in CO₂ hydrogenation to heavy olefins. The FeK/SWNTs catalyst also exhibited a minor change in catalytic performance in a 120 h stability test, highlighting SWNTs as a promising catalyst support for producing value-added chemicals from greenhouse gas CO₂.