We describe a way of generating films (<2 mm2; <40 μm thick) of aligned Fe-filled carbon nanotubes. These Fe nanowires are usually composed of single Fe crystals, and have dimensions from 5–40 nm outer diameter and <10 μm in length. The carbon tubes, which coat the wires, have external diameters of ∼20–70 nm and are <40 μm in length. High-resolution electron energy loss spectroscopy, x-ray powder diffraction, and elemental mapping of the tubular structures reveal only characteristic metallic signals and the effective absence of oxygen (or any other nonmetallic element) within the wires. The material exhibits coercivities in the 430–1070 Oe range, i.e., greater than those reported for Ni and Co nanowires.

The technology is available to produce fuel ethanol from renewable lignocellulosic biomass. The current challenge is to assemble the various process options into a commercial venture and begin the task of incremental improvement. Current process designs for lignocellulose are far more complex than grain to ethanol processes. This complexity results in part from the complexity of the substrate and the biological limitations of the catalyst. Our work at the University of Florida has focused primarily on the genetic engineering of Enteric bacteria using genes encoding Zymomonas mobilis pyruvate decarboxylase and alcohol dehydrogenase. These two genes have been assembled into a portable ethanol production cassette, the PET operon, and integrated into the chromosome of Escherichia coli B for use with hemicellulose-derived syrups. The resulting strain, KO11, produces ethanol efficiently from all hexose and pentose sugars present in the polymers of hemicellulose. By using the same approach, we integrated the PET operon into the chromosome of Klebsiella oxytoca to produce strain P2 for use in the simultaneous saccharification and fermentation (SSF) process for cellulose. Strain P2 has the native ability to ferment cellobiose and cellotriose, eliminating the need for one class of cellulase enzymes. Recently, the ability to produce and secrete high levels of endoglucanase has also been added to strain P2, further reducing the requirement for fungal cellulase. The general approach for the genetic engineering of new biocatalysts using the PET operon has been most successful with Enteric bacteria but was also extended to Gram positive bacteria, which have other useful traits for lignocellulose conversion. Many opportunities remain for further improvements in these biocatalysts as we proceed toward the development of single organisms that can be used for the efficient fermentation of both hemicellulosic and cellulosic substrates.

The reduction behavior of Co/TiO 2 and Co/Mn/TiO 2 catalysts for Fischer-Tropsch synthesis has been investigated by soft X-ray absorption spectroscopy (XAS). In situ XAS measurements of the L 2,3 edges of Co and Mn have been carried out during reduction treatments of the samples in H 2 at a pressure of 2 mbar and at temperatures up to 425°C. The changes of Co and Mn 3d valences and the symmetries throughout the reduction have been determined by comparison with theoretical calculations based on the charge transfer multiplet code. Furthermore, bulk Co 3 O 4 has been reduced under the same conditions to evaluate the effect of TiO 2 as a support on the reducibility of Co oxides. The average Co valence at the various temperatures has been determined from a linear combination of the reference spectra. It was found that the unsupported Co 3 O 4 was easily reduced to Co 0 at 425°C, whereas the Co 3 O 4 supported on TiO 2 catalysts was only reduced to a mixture of CoO and Co 0 , even after 12 h reduction at 425°C. The presence of Mn further retards the reduction of the supported Co 3 O 4 particles. The Mn III ions were easily reduced to MnO at temperatures lower than 300°C, and they remained in this oxidation state even after further temperature increase. In addition, catalytic tests in the Fischer-Tropsch synthesis reaction at a pressure of 1 bar indicate that the selectivity of these catalysts might be related to the extent of Co reduced after the activation treatment (i.e., the reduction with H 2 ).

The adsorption properties of manganese-promoted Co/TiO 2 Fischer-Tropsch (FT) catalysts were investigated by diffuse reflectance infrared spectroscopy (DRIFTS) using CO and H 2 as probe molecules. Manganese was found to be closely associated to the FT active Co 0 sites at the surface of the catalysts. With increased MnO loading, CO preferentially binded linearly to surface metal sites. Manganese also decreased the extent of Co-TiO 2 interactions, increasing the Co 0 dispersion, resulting in higher H 2 chemisorption uptake. Furthermore, with increasing MnO loading, FT catalytic tests at 1 bar and 220 • C revealed an increase in C 5+ selectivity and olefinic products. These findings suggest that MnO species induce both structural and electronic promotion effects, resulting in higher metal dispersions and lower hydrogenation activity of the catalyst, ultimately enhancing the overall FT catalytic performance. The findings also suggest that MnO catalyzes the water-gas shift reaction, thereby changing the syngas feed composition and affecting overall catalyst performance.

The effects of the addition of manganese to a series of TiO 2 -supported cobalt Fischer-Tropsch (FT) catalysts prepared by different methods were studied by a combination of X-ray diffraction (XRD), temperatureprogrammed reduction (TPR), transmission electron microscopy (TEM), and in situ X-ray absorption fine structure (XAFS) spectroscopy at the Co and Mn K-edges. After calcination, the catalysts were generally composed of large Co 3 O 4 clusters in the range 15-35 nm and a MnO 2 -type phase, which existed either dispersed on the TiO 2 surface or covering the Co 3 O 4 particles. Manganese was also found to coexist with the Co 3 O 4 in the form of Co 3-x Mn x O 4 solutions, as revealed by XRD and XAFS. Characterization of the catalysts after H 2 reduction at 350°C by XAFS and TEM showed mostly the formation of very small Co 0 particles (around 2-6 nm), indicating that the cobalt phase tends to redisperse during the reduction process from Co 3 O 4 to Co 0 . The presence of manganese was found to hamper the cobalt reducibility, with this effect being more severe when Co 3-x Mn x O 4 solutions were initially present in the catalyst precursors. Moreover, the presence of manganese generally led to the formation of larger cobalt agglomerates (∼8-15 nm) upon reduction, probably as a consequence of the decrease in cobalt reducibility. The XAFS results revealed that all reduced catalysts contained manganese entirely in a Mn 2+ state, and two well-distinguished compounds could be identified: (1) a highly dispersed Ti 2 MnO 4 -type phase located at the TiO 2 surface and (2) a less dispersed MnO phase being in the proximity of the cobalt particles. Furthermore, the MnO was also found to exist partially mixed with a CoO phase in the form of rock-salt Mn 1-x Co x O-type solid solutions. The existence of the later solutions was further confirmed by scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) for a Mn-rich sample. Finally, the cobalt active site composition in the catalysts after reduction at 300 and 350°C was linked to the catalytic performances obtained under reaction conditions of 220°C, 1 bar, and H 2 /CO ) 2. The catalysts with larger Co 0 particles (∼ >5 nm) and lower Co reduction extents displayed a higher intrinsic hydrogenation activity and a longer catalyst lifetime. Interestingly, the MnO and Mn 1-x Co x O species effectively promoted these larger Co 0 particles by increasing the C 5+ selectivity and decreasing the CH 4 production, while they did not significantly influence the selectivity of the catalysts containing very small Co 0 particles.

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STEM-EELS and EXAFS have been used to investigate the location and electronic state of Mn as promoter in TiO2-supported cobalt Fischer-Tropsch catalysts prepared by two different procedures. It was found that the extent of interaction between Mn and the active Co phase as well as the level of Mn dispersion over the TiO2 surface largely determine the enhancement of the selectivity in the Fischer-Tropsch synthesis at pressures of 1 bar.