CO Hydrodeoxygenation On Functionalized Metal-Free CNT Surfaces

CO hydro-deoxygenation can lead to products such as hydrocarbons (obtained through Fischer Tropsch Synthesis) and oxygenates (such as alcohols ketones and aldehydes) as well as cyclic and aromatic compounds.  The long carbon chain moieties of these organic compounds have significant importance as fuels.  Traditionally , late transition metals such as iron and cobalt are use as active catalysts with a number of promoters that affect the reducibility of these metals and on the activity and selectivity.  Herein , we report the results of the experimental and theoretical investigations on CO hydro-deoxygenation and subsequent chain growth on metal free CNT surfaces functionalized with C-O , COOH , OH and N.  Experimental data showed that these catalysts prepared by air assisted CVD show significant enhancement (1-3 orders higher) in the rate of conversion as compared to a simple Fe-Zn-K catalyst supported on gamma alumina that was produced by precipitation-impregnation method.  XPS data show no Fe (catalyst for CNT growth) signature and it was concluded that the Fe , if present , is occluded from the reactants.  The experimental data and XPS showed that the reaction rates correlated well with the oxygen containing functional groups on the CNT molecules.  The Raman spectra also showed that an increase in the defects improved the conversion rates.  The TGA data show that the occluded iron was less than 1/8th of the amount of that used for the Fe-Zn-K catalyst.  A complete characterization of the experimental conditions was conducted and it was observed that the activity of the CNT catalysts ranged from 200 – 450 oC.  It was observed that the product distribution could be tuned to obtain oxygenates or linear chain hydrocarbons by adjusting the reaction temperature or pressure.  DFT calculations conducted independently showed that C=O or OH functional groups are essential for the progress of this reaction.  It was calculated that while pristine CNTs could not chemisorb CO or H2 , CO could be chemisorbed on to epoxy or COOH sites.  It was also seen that the hydrogen insertion could not occur from the gas phase and the mechanism required the presence of OH groups which could be present on the as produced material or be produced as a result of dissociative adsorption of hydrogen molecule at the epoxy site.  The DFT calculations showed that the curvature of the CNT would affect the rates of the reaction.  Experimental results on SWNT and graphene will also be presented and compared with the DFT findings.  Finally the comparison of the experimental data and the DFT predictions on nitrogen doped CNTs as well as the performance of these caatlysts loaded on various substrates will be presented.  The data will show that these alternate , renewable catalysts can efficiently effect the hydro-deoxygenation of CO and assist in subsequent chain growth.