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 μmolCO2 gFe–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.