Efficient hierarchically structured composites containing cobalt catalyst for clean synthetic fuel production from Fischer-Tropsch synthesis

We report a straightforward preparation method to synthesize hierarchical composite consisting of TiO2-coated multi-walled carbon nanotubes (CNTs) decorating a macroscopic host structure of alpha-Al2O3. The obtained composite possesses moderate specific surface area and very open porous structure, as well as moderate interaction with active sites, which significantly improve the cobalt nanoparticles dispersion and the mass diffusion during the reaction. The Co/TiO2/CNT-alpha-Al2O3 (CoTiCNTA) catalyst is then used in the Fischer-Tropsch synthesis (FTS) process. This hierarchical catalyst achieves a FTS rate to C5+ of 0.80 g(C5+) g(cat)(-1) h(-1) along with a long-chain hydrocarbons (C5+) selectivity of 85%, which can be pointed out as the most outstanding noble promoter-free catalyst for the FTS process. The as-synthesized catalyst also exhibits an extremely high stability as a function of time on stream which is also one of the prerequisites for the development of future FTS catalysts, especially for the Biomass-to-Liquids process where trace amount of impurities and/or moisture could have an impact on the catalyst stability. The present work also introduces a new investigation methodology based on the use of zero field Co-59 NMR, which allows one to map in a precise manner the cobalt active phase distribution and to correlate it with the FTS performance. It is expected that such technique would be extremely helpful for the understanding of the catalyst structure-performance relationship and for future optimization in the FTS process as well as in other fields of investigation where cobalt particles are involved. (C) 2014 Elsevier Inc. All rights reserved

Towards nanoprinting with metals on graphene

Graphene and carbon nanotubes are envisaged as suitable materials for the fabrication of the new generation of nanoelectronics. The controlled patterning of such nanostructures with metal nanoparticles is conditioned by the transfer between a recipient and the surface to pattern. Electromigration under the impact of an applied voltage stands at the base of printing discrete digits at the nanoscale. Here we report the use of carbon nanotubes as nanoreservoirs for iron nanoparticles transfer on few-layer graphene. An initial Joule-induced annealing is required to ensure the control of the mass transfer with the nanotube acting as a `pen' for the writing process. By applying a voltage, the tube filled with metal nanoparticles can deposit metal on the surface of the graphene sheet at precise locations. The reverse transfer of nanoparticles from the graphene surface to the nanotube when changing the voltage polarity opens the way for error corrections

Direct Synthesis of TiN/Mesoporous Carbon Nanocomposite by Nitridation of a Hybrid Inorganic/Organic Mesostructured Material

A titanium nitride (TiN)/mesoporous carbon nanocomposite with a high surface area (320 m2/g) has been successfully synthesized by a direct route based on a concomitant polymerization of organic and inorganic species (phenolformaldehyde resin and TiO2-based oligomers, respectively). These polymers self-assemble in the presence of a pore-structuring agent, an amphiphilic copolymer ((poly(ethylene oxide))106(poly(propylene oxide))70(poly(ethylene oxide))106) during the solvent evaporation step and yield to an ordered mesostructured hybrid organic/inorganic materials. Its heat treatment in ammonia led to the carbonization of the organic part and to the nitridation of the TiO2-based part. A TiN/mesoporous C nanocomposite constituted of TiN (61 wt%) nanocrystallites (from 10 to 50 nm in diameter) embedded into a mesoporous carbon matrix was obtained

Silicon carbide coated with TiO2 with enhanced cobalt active phase dispersion for Fischer-Tropsch synthesis

The introduction of a thin layer of TiO2 on beta-SiC allows a significant improvement of the cobalt dispersion. This catalyst exhibits an excellent and stable catalytic activity for the Fischer-Tropsch synthesis (FTS) with high C5+ selectivity, which contributes to the development of a new active catalyst family in the gas-to-liquid process

Fischer-Tropsch Reaction on a Thermally Conductive and Reusable Silicon Carbide Support

The Fischer-Tropsch (FT) process, in which synthesis gas (syngas) derived from coal, natural gas, and biomass is converted into synthetic liquid fuels and chemicals, is a strongly exothermic reaction, and thus, a large amount of heat is generated during the reaction that could severely modify the overall selectivity of the process. In this Review, we report the advantages that can be offered by different thermally conductive supports, that is, carbon nanomaterials and silicon carbide, pure or doped with different promoters, for the development of more active and selective FT catalysts. This Review follows a discussion regarding the clear trend in the advantages and drawbacks of these systems in terms of energy efficiency and catalytic performance for this most-demanded catalytic process. It is demonstrated that the use of a support with an appropriate pore size and thermal conductivity is an effective strategy to tune and improve the activity of the catalyst and to improve product selectivity in the FT process. The active phase and the recovery of the support, which also represents a main concern in terms of the large amount of FT catalyst used and the cost of the active cobalt phase, is also discussed within the framework of this Review. It is expected that a thermally conductive support such as -SiC will not only improve the development of the FT process, but that it will also be part of a new support for different catalytic processes for which high catalytic performance and selectivity are strongly needed

Single crystals of mesoporous tungstenosilicate W-MCM-48 molecular sieves for the conversion of methylcyclopentane (MCP)

Highly ordered W-MCM-48 mesoporous materials containing isolated W atoms in tetrahedral framework positions were successfully synthesized following the S+I- pathway, up to a Si/W of 40. When tungsten content was increased up to a Si/W of 20, the ordered cubic structure was only partially maintained, and for a Si/W of 10 an amorphous phase was obtained. Highly isolated tetrahedral framework tungsten atoms in the W-MCM-48 with a Si/W of 40, have been identified by UV-vis band at 225 nm, IR-TF band at 970cm(-1) and XRD. The W 4f XPS results suggest that the tungsten atoms exist in two oxidation states, W4+ and W5+. The morphology of the samples varies as a function of tungsten content. The W-MCM-48 samples with a Si/W ratio of 40 existed as crystals with a unique crystalline morphology consisting of cubes truncated rhombic dodecahedrons belonging to the cubic Ia3d space group, while the samples with a Si/W ratio of 20 exhibited a different morphology consisting of spheres and cubes truncated by rhombic dodecahedrons. A comparison of samples with Si/W of infinity, Si/W of 40 and Si/W of 20 was performed using the conversion of MCP carried out at 450 degrees C under H-2. (C) 2010 Elsevier B. V. All rights reserved

Structure and Sorption Properties of a Zeolite-Templated Carbon with the EMT Structure Type

An ordered microporous carbon material was prepared by the nanocasting process using the EMC-2 zeolite (EMT structure type) as a hard template. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed long-range ordering in the material that resulted from the negative replication of the host template. The carbon porous network replicating the zeolite structure was modeled by overlapped spherical voids with diameters determined from the XRD pattern that displayed up to six distinct peaks. The surface delimiting the 3D interconnected porosity of the solid has a complex morphology. The pore size distribution calculated from the XRD-derived structural model is characterized by a maximum at 1.04 nm related to the long-range-ordered microporous network. Complementary studies by immersion calorimetry revealed that most of the porosity was characterized by a size above 1.5 nm. These porous features were compared to data resulting from classical analysis (DR, DFT, BET, etc.) of the N-2 (77 K) and CO2 (low and high pressure, 273 K) physisorption isotherms. The limitations of these approaches are discussed in light of the pore size distribution consistently determined by XRD and immersion calorimetry measurements

Microstructural Analysis and Energy-Filtered TEM Imaging to Investigate the Structure-Activity Relationship in Fischer-Tropsch Catalysts

We present herein the application of chemical imaging based on energy-filtered TEM in 2D and 3D modes to determine the distribution of phases in Co/TiO2-SiC catalysts used in Fischer-Tropsch synthesis. In combination with more traditional techniques such as high-resolution TEM imaging, it allowed us to precisely characterize the microstructure and the relative distribution of the three compounds, Co, Si, and Ti, before and after the catalytic reaction. We show that the TiO2 doping was almost homogenous within the bimodal porous structure of -SiC. The characteristics of the cobalt nanoparticles depended on the phase they are in contact with: small nanoparticles are found on TiO2 and larger nanoparticles close to SiC. Enhancement of the catalytic performance and higher stability were observed for the Co/TiO2-SiC catalyst relative to Co/SiC, which was attributed to the better dispersion of cobalt on TiO2-doped SiC support and to the relatively strong Co-TiO2 interaction. From a general point of view, this work illustrates that the advanced TEM-based techniques are unavoidable for the characterization and the optimization of heterogeneous catalysts

3D-TEM investigation of the nanostructure of a delta-Al2O3 catalyst support decorated with Pd nanoparticles

The electron tomography technique applied in a quantitative way allowed us to characterize a heterogeneous catalyst made of Pd nanoparticles deposited on a delta-Al2O3 lamellar support. In the first step, high resolution tomographic experiments carried out on several typical areas of support have confirmed the hypothesis of formation of delta-Al2O3 proposed in the literature by the coalescence of lateral facets of the gamma-Al2O3 precursor. A bimodal porosity was also observed in the arrangement of delta-Al2O3 platelets. In the second step, the Pd nanoparticles were found preferentially anchored on the lateral facets of delta-Al2O3 platelets or on the defects situated on their basal planes. From a general point of view, we have demonstrated once again that the electron tomography technique implemented with nanometre resolution provides unique insight into the structure, morphology and spatial arrangement of components in a complex 3D nanostructure

Ecofriendly synthesis of ceria foam via carboxymethylcellulose gelation: application for the epoxidation of chalcone

A simple and innovative process is described for the ecofriendly preparation of ceria foams via carboxymethylcellulose gelation by Ce4+ cations; heat treatment of the ensuing xerogels produces ceria foams. The influence of the concentration of cerium and of the calcination temperature of the xerogels is studied. Several characterization methods have been used and the obtained results demonstrate that this technique allows the controlled growth of ceria foams. The foamy structure apparently is responsible for UV absorption, and the ceria foam is basic enough to promote the epoxidation of chalcone; comparison of the catalytic activity of the ceria foam versus ceria prepared via a coprecipitation method shows that the ceria foam is most active as it promotes epoxidation of electron-deficient alkenes with dilute aqueous hydrogen peroxide