Andrei Y. Khodakov
university of lille
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Featured researches published by Andrei Y. Khodakov.
Angewandte Chemie | 2008
Wei Chu; Li‐Nan Wang; P. A. Chernavskii; Andrei Y. Khodakov
In the last twenty years, remarkable advances in nanosciences and nanotechnology have given an impulse to the design of heterogeneous catalysts. Bell emphasized in 2003 the role of nanoparticle size in catalyst performance, and Schl#gl and Abd Hamid proposed in 2004 that the synthesis of nanosized catalysts may require multidimensional structural control. Glow-discharge (luminous) plasma is obtained by applying a potential difference between two electrodes placed in a gas. The plasma provides energy for decomposition of metal precursors. Several active catalysts have been developed by using glow discharge. The glow-discharge activation process is simple, quick, audio-visual, and easy to control. It does not require the high temperatures and significant amounts of compressed gases which are typically used in conventional catalyst pretreatments. The increasing interest in Fischer–Tropsch (FT) synthesis has been due to the growing demand for clean fuels and utilization of abundant natural gas, coal, and biomass-derived synthesis gas. Cobalt catalysts are preferred for FT synthesis due to their high productivity, high selectivity for heavy hydrocarbons, high stability, and low activity in the water-gas shift reaction. The catalytic performance of cobalt catalysts in FT synthesis appears to be strongly affected by the size of the cobalt metal particles. Conventional cobalt FT catalysts are prepared by aqueous impregnation of supports (silica, alumina, titania, etc.) with solutions of cobalt salts. After decomposition of the supported cobalt salts by calcination in an oxidizing atmosphere, the catalysts are reduced in hydrogen to generate cobalt metal sites. The present work focuses on the effects of pretreatment with glow-discharge plasma on cobalt dispersion and reducibility in alumina-supported catalysts and their performance in FT synthesis. Details of catalyst preparation are given in the Experimental Section. Cobalt and platinum contents in catalysts were 15 wt% and 0.1 wt%, respectively. The conventionally calcined catalysts are denoted Co(Pt)-Al2O3-T, where T indicates the temperature of the calcination pretreatment and Pt indicates promotion with Pt. The monometallic and Pt-promoted catalysts that were prepared using glowdischarge plasma (shortened to: plasma-assisted catalysts) are designated Co-Al2O3-PNH and CoPt-Al2O3-PNH respectively (Table 1).
Angewandte Chemie | 2013
Vincenzo Roberto Calderone; N. R. Shiju; Daniel Curulla-Ferré; Stéphane Chambrey; Andrei Y. Khodakov; Amadeus Rose; Johannes Thiessen; Andreas Jess; Gadi Rothenberg
Audio cassettes hold the key to enhancing Fischer–Tropsch catalysis. Catalysts based on ultra‐thin cobalt shells surrounding cheap iron oxide cores (see picture) are developed, an approach previously optimized for preparing magnetic tape for audio cassettes. These particles are easily made on a large scale, and are excellent Fischer–Tropsch catalysts, giving good diesel fractions.
Journal of Materials Chemistry | 2009
Hui Zhang; Christine Lancelot; Wei Chu; Jingping Hong; Andrei Y. Khodakov; P. A. Chernavskii; Jian Zheng; Dongge Tong
The nature of cobalt species in the catalysts supported by multi-wall carbon nanotubes and their catalytic performance in Fischer–Tropsch synthesis were investigated using nitrogen adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, in situ magnetic method, X-ray absorption and temperature programmed reduction. The catalysts were prepared by incipient wetness impregnation using solutions of cobalt nitrate assisted by sonochemical process followed by calcination in nitrogen. The characterization techniques uncovered that acid pretreatment oxidized the carbon nanotube surface and removed impurities. Small cobalt oxide particles of 8–10 nm diameter and irregular shape anchored to the outer surface of carbon nanotubes were detected in the calcined samples by several characterization techniques. The catalysts displayed high cobalt reducibility, which was slightly affected by the pretreatment with nitric acid and nanotube outer diameter. Cobalt catalysts supported on carbon nanotubes exhibited high catalytic activity in Fischer–Tropsch synthesis. Pretreatment with nitric acid leads to a 25% increase in hydrocarbon yield, while carbon nanotube diameter does not seem to significantly affect the Fischer–Tropsch performance of the resulting catalysts.
Advances in Colloid and Interface Science | 2008
Vladimir L. Zholobenko; Andrei Y. Khodakov; Marianne Impéror-Clerc; D. Durand; Isabelle Grillo
This work presents an overview of the data obtained for SBA-15 synthesis under the reaction conditions using synchrotron based small angle X-ray scattering and small angle neutron scattering. Three major stages in the synthesis of SBA-15 materials proceeding according to the cooperative self-assembly mechanism have been identified, and the structures of the intermediates species have been established. Our in situ time-resolved neutron scattering experiments demonstrate that only spherical micelles of the templating agent are present in the synthesis mixture during the first stage of the reaction. According to the neutron scattering and X-ray scattering data, in the second stage of the reaction the formation of hybrid organic-inorganic micelles is accompanied with the transformation from spherical to cylindrical micelles, which takes place before the precipitation of the ordered SBA-15 phase. During the third stage, these micelles aggregate into a two-dimensional hexagonal structure, confirming that the precipitation takes place as the result of self-assembly of the hybrid cylindrical micelles. As the synthesis proceeds, the voids between the cylinders are filled with the silicate species which undergo condensation reactions resulting in cross-linking and covalent bonding, leading to the formation of highly ordered SBA-15 mesostructure. This work demonstrates that valuable structural information can be obtained from X-ray and neutron scattering characterisation of complex systems containing periodic phases with d-spacing values up to 30 nm, and that both techniques are powerful means for in situ monitoring of the formation of nanostructured materials.
Studies in Surface Science and Catalysis | 2002
Andrei Y. Khodakov; Rafeh Bechara; Anne Griboval-Constant
The structure of cobalt catalysts supported by periodic mesoporous silicas at different stages of preparation was characterized by XRD, N 2 adsorption, XPS, in situ X-ray absorption and TGA. It was shown that the size and reducibility of supported cobalt particles were strongly affected by porous structure; larger and more easily reducible particles being detected in wider pore silicas. Cobalt dispersion was found to be controlled by silica pore sizes even at high cobalt contents (up to 30 wt.%) It was shown that catalytic behavior of cobalt supported mesoporous silicas in Fischer Tropsch synthesis strongly depended on cobalt dispersion and catalyst porous structure. Wide pore SBA-15 supported Co catalysts were found to be much (about 5–10 times) more active than narrow pore MCM-41 supported catalysts with the same cobalt content. Product distribution was found to be a function of cobalt particle sizes and cobalt reducibility. Fischer Tropsch reaction rates increased monotonically with increase in cobalt content up to 30 wt %, whereas product distributions for completely reduced wide pore catalysts were nearly the same at high and low cobalt loadings.
Catalysis Science & Technology | 2015
Vitaly V. Ordomsky; Benoit Legras; K. Cheng; Sébastien Paul; Andrei Y. Khodakov
High reactivity of iron carbides enhances the Fischer–Tropsch reaction rate on supported iron catalysts. Highly dispersed carbide is easily hydrogenated to methane in a hydrogen atmosphere with subsequent regeneration in the presence of CO. Carbon atoms in iron carbide are involved in the initiation of chain growth in Fischer–Tropsch synthesis.
Brazilian Journal of Physics | 2009
Andrei Y. Khodakov
Fischer-Tropsch synthesis is a part of Gas-to Liquids (GTL), Biomass-to-Liquids (BTL) and Coal to Liquids (CTL) technologies, which produce alternatives clean fuels from natural gas, biomass and coal. The catalytic performance of cobalt catalysts in Fischer-Tropsch synthesis strongly depends on the size of cobalt particles in nanoscale range (6-30 nm). Cobalt catalysts are usually prepared via incipient wetness impregnation using cobalt salts (cobalt precursors). Catalyst preparation involves several important steps. The paper shows that decomposition of cobalt precursors is often a crucial step in the catalyst design; slower rate of decomposition of cobalt precursors favors smaller size of cobalt particles, higher cobalt dispersion and enhances catalytic performance in Fischer-Tropsch synthesis.
Chemical Communications | 2007
Marianne Impéror-Clerc; Isabelle Grillo; Andrei Y. Khodakov; D. Durand; Vladimir L. Zholobenko
Time-resolved in situ SANS investigations have provided direct experimental evidence for the three initial steps in the formation of the SBA-15 mesoporous material: an induction period is followed by a shape transformation of the micelles from spherical to cylindrical ones followed by the precipitation of a two-dimensional hexagonal phase.
Chemcatchem | 2014
Jorge M. Beiramar; Anne Griboval-Constant; Andrei Y. Khodakov
A series of CuZnAl catalysts modified with different promoters (Fe, Co, Ru, Zr, Mo, Mg, Mn, and Cr) have been prepared through co‐precipitation, characterised by applying a combination of techniques, and tested for carbon monoxide hydrogenation. Cu reducibility in CuZnAl catalysts was affected by the addition of promoters. The ease of Cu reduction in the promoted catalysts leads to more active catalysts for the hydrogenation of carbon monoxide and the production of C2+ alcohols, whereas lower catalytic activity was observed over less reducible catalysts. The promotion of CuZnAl catalysts even with small amounts of Cr, Mn, and Fe resulted in a significant modification in the reaction selectivity. The Fe‐containing catalyst demonstrated a dramatic increase in carbon monoxide conversion and C2+ alcohol productivity (30 mg g
Studies in Surface Science and Catalysis | 2004
Andrei Y. Khodakov; J.S. Girardon; Anne Griboval-Constant; A. S. Lermontov; P. A. Chernavskii
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