Synthesis and use of carbon nanotubes as a support for the Fischer-Tropsch Synthesis.

Abstract Carbon nanotubes (CNTs) were grown catalytically by a chemical vapor deposition method and characterized by a range of techniques. Fe, Ru and Co catalysts supported on the carbon nanotubes were prepared and investigated for their performances in the Fischer-Tropsch synthesis. CNTs were synthesized in a quartz tubular reactor at atmospheric pressure and at temperatures of 700°C over iron supported on CaCO3 using C2H2 as carbon source. Prior to CNT synthesis, the iron catalyst was first reduced under the same conditions (700°C and atmospheric pressure) in a flow of 5% H2 balanced in Argon. The catalyst, for the preparation of the CNTs, was prepared by the incipient wetness impregnation. The purification of the CNTs was performed with 30 wt % HNO3. Characterization of the CNTs using TEM, SEM, HRTEM, BET and TPR revealed that the crude product contained solely CNTs, catalysts particles and support, while no amorphous carbon was observed. The purified product is comprised of an interwoven matrix of tubes that were shown to be multi-walled (MWCNTs). CNT supported FT based catalysts were also prepared by an incipient wetness impregnation method and tested in a plug flow reactor in Fischer-Tropsch synthesis. The TEM images of the different FT catalysts supported on CNTs revealed that the catalyst particles are well dispersed on the surface of the CNTs. The catalyst particles were very iii small, and some residual Fe catalyst material, not removed by the acid treatment, could clearly be seen on the surface of the CNTs. The reduction and metal dispersion properties of the catalysts were investigated through TPR and chemisorption techniques. A TPR study showed three reduction steps for Co catalysts, and addition of Ru to the catalyst decreased the reduction temperature of the catalysts. Gasification of the CNTs was noted to occur at temperatures higher than 600°C. The effect of metal catalyst loading and promoters on the activity and selectivity of CNT supported FT synthesis catalysts was studied under condition of 275°C, 8 bar, CO/H2 = 1/2 and different flow rates. The FT catalysts supported on carbon nanotubes displayed a high CO conversion and excellent stability with time on stream in the Fischer-Tropsch synthesis. Fe catalysts displayed the lowest methane selectivity compared to all other FT synthesis catalysts used in this study

Towards Carbon Neutral CO2 Conversion to Hydrocarbons

With fossil fuels still predicted to contribute close to 80 % of the primary energy consumption by 2040, methods to limit further CO2 emissions in the atmosphere are urgently needed to avoid the catastrophic scenarios associated with global warming. In parallel with improvements in energy efficiency and CO2 storage, the conversion of CO2 has emerged as a complementary route with significant potential. In this work we present the direct thermo‐catalytic conversion of CO2 to hydrocarbons using a novel iron nanoparticle–carbon nanotube (Fe@CNT) catalyst. We adopted a holistic and systematic approach to CO2 conversion by integrating process optimization—identifying reaction conditions to maximize conversion and selectivity towards long chain hydrocarbons and/or short olefins—with catalyst optimization through the addition of promoters. The result is the production of valuable hydrocarbons in a manner that can approach carbon neutrality under realistic industrial process conditions