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

Controlled and Chemoselective Hydrogenation of Nitrobenzene over Ru@C60 Catalysts

cited By 15International audienceElectron-deficient ruthenium nanoparticles supported on Ru fulleride nanospheres allow the successive and chemoselective hydrogenation of nitrobenzene to aniline and then to cyclohexylamine. The catalysts were prepared in a straightforward manner by decomposition under dihydrogen of [Ru(COD)(COT)] in the presence of C60. The nitrobenzene hydrogenation reaction is solvent sensitive and proceeds more quickly in methanol than in other alcohols. The same behavior, i.e. a two-step successive hydrogenation, has been observed for several substituted nitroarenes. Density functional theory calculations suggest that the observed chemoselectivity is mainly governed by the presence of surface hydrides on the electron-deficient Ru nanoparticles. At the threshold value of 1.5 H per Ru surface atom, the formation of aniline is favored due to the net preference of the NO2 coordination

Understanding the surface chemistry of carbon nanotubes: Toward a rational design of Ru nanocatalysts

International audienceA comprehensive experimental and theoretical study of the surface chemistry of ruthenium nanoparticles supported on/in multi-walled carbon nanotubes (CNTs) is reported that could pave the way to the rational design of metal–carbon nanocomposites. It is shown that the oxidation of CNTs by nitric acid that creates various oxygen surface functional groups (SFGs) on the CNT external surface is a crucial step for metal grafting. In particular, it is demonstrated that carboxylic acid, carboxylic anhydride, and lactone groups act as anchoring centers for the Ru precursor, presumably as surface acetato ligands. The HNO3 treatment that also allows CNT opening contributes to the endohedral Ru deposition. The stability of Ru nanoparticles, modeled by a Ru13 cluster, on different adsorption sites follows the order: Gr-DV-(COOH)2 > Gr-DV > Gr (where DV is a double vacancy and Gr the graphene surface). It is evidenced that, after a high-temperature treatment performed in order to remove the SFGs, the Ru/CNT material can react with oxygen from air via a surface reconstruction reaction, which reforms a stable Ru-acetato interface. The mechanism of this reaction has been investigated by DFT. These Ru/CNT catalysts are extremely stable, keeping a mean particle size <2 nm, even after heating at 973 K under a hydrogen atmosphere

Understanding the surface chemistry of carbon nanotubes: Toward a rational design of Ru nanocatalysts

International audienceA comprehensive experimental and theoretical study of the surface chemistry of ruthenium nanoparticles supported on/in multi-walled carbon nanotubes (CNTs) is reported that could pave the way to the rational design of metal–carbon nanocomposites. It is shown that the oxidation of CNTs by nitric acid that creates various oxygen surface functional groups (SFGs) on the CNT external surface is a crucial step for metal grafting. In particular, it is demonstrated that carboxylic acid, carboxylic anhydride, and lactone groups act as anchoring centers for the Ru precursor, presumably as surface acetato ligands. The HNO3 treatment that also allows CNT opening contributes to the endohedral Ru deposition. The stability of Ru nanoparticles, modeled by a Ru13 cluster, on different adsorption sites follows the order: Gr-DV-(COOH)2 > Gr-DV > Gr (where DV is a double vacancy and Gr the graphene surface). It is evidenced that, after a high-temperature treatment performed in order to remove the SFGs, the Ru/CNT material can react with oxygen from air via a surface reconstruction reaction, which reforms a stable Ru-acetato interface. The mechanism of this reaction has been investigated by DFT. These Ru/CNT catalysts are extremely stable, keeping a mean particle size <2 nm, even after heating at 973 K under a hydrogen atmosphere

Characterization of cobalt phosphide nanoparticles derived from molecular clusters in mesoporous silica

The synthesis of well dispersed cobalt phosphide nanoparticles (NPs) in SBA-15 mesoporous silica by wet impregnation of the molecular cluster [Co4(CO)10(μ-dppa)] (1) (dppa = HN(PPh2)2) is described. The thermal activation of the silica impregnated precursor under a H2/N2 (5/95 %) stream at different temperatures to form NPs was studied and it was found that the size of the latter is limited in the 5.5–6.5 nm range by the size of the pores. The obtained materials were characterized by various analytical methods. The porosity and the structure of the mesoporous silica supports were analyzed by N2 adsorption/desorption and small-angle X-ray diffraction. The nanoparticles were characterized by wide-angle X-ray diffraction, transmission electron microscopy in conventional and scanning modes, electron tomography, energy-dispersive X-ray spectroscopy, and magnetic measurements. Cobalt phosphide NPs of few nanometers were observed in the pores of SBA-15

Controlled and Chemoselective Hydrogenation of Nitrobenzene over Ru@C₆₀ Catalysts

Electron-deficient ruthenium nanoparticles supported on Ru fulleride nanospheres allow the successive and chemoselective hydrogenation of nitrobenzene to aniline and then to cyclohexylamine. The catalysts were prepared in a straightforward manner by decomposition under dihydrogen of [Ru­(COD)­(COT)] in the presence of C₆₀. The nitrobenzene hydrogenation reaction is solvent sensitive and proceeds more quickly in methanol than in other alcohols. The same behavior, i.e. a two-step successive hydrogenation, has been observed for several substituted nitroarenes. Density functional theory calculations suggest that the observed chemoselectivity is mainly governed by the presence of surface hydrides on the electron-deficient Ru nanoparticles. At the threshold value of 1.5 H per Ru surface atom, the formation of aniline is favored due to the net preference of the NO₂ coordination

Nonalcoholic Fatty Liver Disease and Type 2 Diabetes Mellitus: A Bidirectional Relationship

Worldwide, the leading cause of chronic liver disease is represented by nonalcoholic fatty liver disease (NAFLD) which has now become a global epidemic of the 21st century, affecting 1 in 4 adults, and which appears to be associated with the steadily increasing rates of metabolic syndrome and its components (obesity, type 2 diabetes mellitus (T2DM), and dyslipidemia). NAFLD has been reported to be associated with extrahepatic manifestations such as cardiovascular disease, T2DM, chronic kidney disease, extrahepatic malignancies (e.g., colorectal cancer), endocrine diseases (e.g., hypothyroidism, polycystic ovarian syndrome, psoriasis, and osteoporosis), obstructive sleep apnea, and iron overload. The prevalence of NAFLD is very high, affecting 25–30% of the world population and encloses two steps: (1) nonalcoholic fatty liver (NAFL), which includes steatosis only, and (2) nonalcoholic steatohepatitis (NASH) defined by the presence of steatosis and inflammation with hepatocyte ballooning, with or without fibrosis which can progress to liver fibrosis, hepatocellular carcinoma, and liver transplantation. Current data define a more complex relationship between NAFLD and T2DM than was previously believed, underlining a bidirectional and mutual association between the two entities. This review aims to summarize the current literature regarding the incidence of T2DM among patients with NAFLD and also the prevalence of NAFLD in T2DM patients, highlighting the recent key studies. Clinicians should screen, diagnose, and treat T2DM in patients with NAFLD in order to avoid short- and long-term complications