K and Mn doped iron-based CO2 hydrogenation catalysts: Detection of KAlH4 as part of the catalyst's active phase

Hydrogenation of CO2 to hydrocarbons is investigated over iron-based catalysts supported on gamma-alumina to produce unsaturated hydrocarbons as feedstock chemicals for jet-fuel synthesis. Over 40% conversion levels can be achieved by doping this catalyst with Mn and K, along with an olefin/paraffin ratio of over 4. The doping levels played a crucial role in the product distribution as well as CO2 conversion yields, with over doping leading to suppression of the desirable hydrocarbon products. The characterization of the catalyst showed the presence of KAlH4 as part of the catalyst's active phase, acting as a reversible H-2 reservoir and as a center for H-2 activation. Characterization of the catalysts by XRD, XPS, and SEM sheds light on the role each dopant had on the overall catalyst's activity and product distribution. (C) 2009 Elsevier B.V. All rights reserved.