Catalytic CO2 hydrogenation to hydrocarbon fuels in a potassium ion-conducting reactor

Abstract

The electrochemically assisted CO2 hydrogenation directly to hydrocarbon fuels was studied, apparently for the first time, over a cheap, widespread and non-precious Fe catalyst in a potassium ion conducting (K-β-Al2O3) reactor, under atmospheric pressure, at relatively low temperatures and using representative concentrated CO2 and H2 gas mixtures and an easily scalable tubular catalyst-electrode configuration. The Fe electrocatalytic film was deposited by dip-coating on a commercial K-β-Al2O3 candle and characterized, both as prepared and after activation and testing, by TPR, TGA, XPS, XRD and SEM-EDX. The optimum operating conditions for both Fe activation (300 ºC, 75% H2, 24 hours) and electropromoted CO2 hydrogenation (300 ºC, 1.5 V, H2/CO2=3) were identified. Long-term tests on electrochemically promoted CO2 hydrogenation to hydrocarbons were performed under selected operating conditions to assess electrocatalyst stability. Both the selectivity to the target product (C5+ hydrocarbons) and the stability of the catalyst can be tuned in situ by modifying the potassium surface coverage via electrochemical pumping of potassium ions through the applied polarization. Finally, as an attempt to improve the catalyst-electrode behaviour, powdered catalysts, based on iron nanoparticles dispersed on KVO3 (a K+ and e- co-conductor) with different Fe loadings (17 and 9 wt%) were prepared and comparatively studied for CO2 hydrogenation to hydrocarbons. The catalyst with higher Fe loading was selected as the most promising, in terms of activity, selectivity and stability, for further catalyst-electrode optimisation by deposition, via dip-coating, of a Fe-KVO3 film on the K-β-Al2O3 candle.