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CO2 hydrogenation to higher hydrocarbons on K/Fe-Al-O spinel catalysts promoted with Si, Ti, Zr, Hf, Mn and Ce

Abstract

Metal oxides grafted on K/Fe-Al-O spinel precursors prepared by co-precipitation in presence of CTAB surfactant displayed significant effects on the performance of the catalysts in CO2 hydrogenation to hydrocarbons. Specifically, 20 wt% titania and 20 wt% zirconia increased the rates of both the reverse water gas shift reaction (RWGS) and the Fischer-Tropsch synthesis (FTS) reflected in the increase of the CO2 conversion and the decrease of CO selectivity. While 20 wt% titania increased methane and C2-C4 selectivity and decreased C5+ selectivity, 20 wt% zirconia displayed no effect on methane and increased C2-C4 and C5+ selectivity. 5 wt% hafnia and 5 wt% manganese oxide had little effect on performance and 5 wt% ceria enhanced the selectivity to both methane and light C2-C4 and decreased significantly C5+. Silica inserted by grafting at the Fe-Al-O surface at 5 wt% acted as promoter of CO2 conversion but at high loading of 15 wt% was a strong inhibitor to FTS, increased methane and CO selectivity and decreased CO2 conversion. Contacting nanoparticles of both spinel and Fe-carbide phases with zirconia caused a decline of electron density of surface iron atoms reflected by increasing of binding energy of Fe (2p) electrons by 0.7-0.8 eV as detected by XPS. This may be a result of strong interaction of iron oxide and zirconia due to incorporation of Zr in the Fe-Al-O spinel structure and strong interaction of near metallic iron in carbide nanocrystals contacting with ZrO2 nanoparticles that play a role of electron acceptor as Lewis acid and explain the increase of CO2 conversion. The extremely low activity of the silica modified catalyst in FTS and enhanced activity in methanation is consistent with the model of selective blocking of the surface iron ions of Fe-carbide component with grafted silica moieties and their interaction with potassium promoter.

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Publication details

The article was received on 04 Jun 2017, accepted on 05 Aug 2017 and first published on 07 Aug 2017


Article type: Paper
DOI: 10.1039/C7CY01118K
Citation: Catal. Sci. Technol., 2017, Accepted Manuscript
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    CO2 hydrogenation to higher hydrocarbons on K/Fe-Al-O spinel catalysts promoted with Si, Ti, Zr, Hf, Mn and Ce

    A. Samanta, M. V. Landau, R. Vidruk and M. Herskowitz, Catal. Sci. Technol., 2017, Accepted Manuscript , DOI: 10.1039/C7CY01118K

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