Synthesis and characterization of niobium-promoted cobalt/iron catalysts supported on carbon nanotubes for the hydrogenation of carbon monoxide
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Abstract: Bimetallic Co/Fe catalysts supported on carbon nanotubes (CNTs) were prepared, and niobium (Nb) was added as promoter to the 70Co:30Fe/CNT catalyst. The physicochemical properties of the catalysts were characterized, and the catalytic performances were analyzed at the same operation conditions (H2:CO (volume ratio)=2:1, p=1 MPa, and t=260 ℃) in a tubular fixed-bed microreactor system. The addition of Nb to the bimetallic catalyst decreases the average size of the oxide nanoparticles and improves the reducibility of the bimetallic catalyst. Evaluation of the catalyst performance in a Fischer-Tropsch reaction shows that the catalyst results in high selectivity to methane, and the selectivity to C5+ increased slightly in the bimetallic catalyst unlike that in the monometallic catalysts. The addition of 1% Nb to the bimetallic catalyst increases CO conversion and selectivity to C5+. Meanwhile, a decrease in methane selectivity is observed.
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Key words:
- Fischer-Tropsch synthesis /
- bimetallic catalyst /
- niobium promoter /
- carbon nanotubes
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Table 1 XPS analysis of 70Co:30Fe/CNT and 1Nb-70Co:30Fe/CNT catalysts
Catalyst XPS binding energy E/eV Co2+/Co3+(atomic ratio) ΔECo Co 2 p1/2 Co 2 p3/2 70Co:30Fe/CNT 795.7 780.2 0.46 15.5 1Nb-70Co:30Fe/CNT 794.6 779.0 0.64 15.6 Table 2 Catalytic activity and products selectivity of catalysts
Catalyst CO conversion x/% CO2 selectivity s/% Product selectivity s/% Olefin/Paraffin C1 C2-4 C5+ Co/CNT 3.0 0.026 80.1 7.1 2.8 0.01 Fe/CNT 2.8 0.025 85.6 13.3 1.5 0.05 70Co30Fe/CNT 3.7 0.026 83.8 12.9 3.3 0.02 1Nb-70Co30Fe/CNT 4.7 0.025 78.1 18.1 3.8 0.04 260 ℃, 1 MPa, H2:CO (volume ratio)=2, SV=51 and 7 h -
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