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Li Wei-xue - One of the best experts on this subject based on the ideXlab platform.

  • Carbon induced selective regulation of cobalt-based Fischer-Tropsch catalysts by ethylene treatment
    2017
    Co-Authors: Zhai Peng, Chen Pei-pei, Xie Jinglin, Liu Jin-xun, Zhao Huabo, Lin Lili, Bo Zhao, Su Hai-yan, Zhu Qingjun, Li Wei-xue
    Abstract:

    Various carbonaceous species were controllably deposited on Co/Al2O3 catalysts using ethylene as carbon source during the activation process for Fischer-Tropsch synthesis (FTS). Atomic, polymeric and graphitic carbon were distinguished by Raman spectroscopy, thermoanalysis and temperature programmed hydrogenation. Significant changes occurred in both the catalytic activity and selectivity toward Hydrocarbon products after ethylene treatment. The activity decreased along with an increase in CH4 selectivity, at the expense of a remarkable decrease of Heavy Hydrocarbon production, resulting in enhanced selectivity for the gasoline fraction. In situ XPS experiments show the possible electron transfer from cobalt to carbon and the blockage of metallic cobalt sites, which is responsible for the deactivation of the catalyst. DFT calculations reveal that the activation barrier (Ea) of methane formation decreases by 0.61 eV on the carbon-absorbed Co(111) surface, whereas the Ea of the CH + CH coupling reaction changes unnoticeably. Hydrogenation of CHx to methane becomes the preferable route among the elementary reactions on the Co(111) surface, leading to dramatic changes in the product distribution. Detailed coke-induced deactivation mechanisms of Co-based catalysts during FTS are discussed

  • Carbon induced selective regulation of cobalt-based Fischer-Tropsch catalysts by ethylene treatment
    FARADAY DISCUSSIONS, 2017
    Co-Authors: Zhai Peng, Chen Pei-pei, Xie Jinglin, Liu Jin-xun, Zhao Huabo, Lin Lili, Bo Zhao, Su Hai-yan, Zhu Qingjun, Li Wei-xue
    Abstract:

    Various carbonaceous species were controllably deposited on Co/Al2O3 catalysts using ethylene as carbon source during the activation process for Fischer-Tropsch synthesis (FTS). Atomic, polymeric and graphitic carbon were distinguished by Raman spectroscopy, thermoanalysis and temperature programmed hydrogenation. Significant changes occurred in both the catalytic activity and selectivity toward Hydrocarbon products after ethylene treatment. The activity decreased along with an increase in CH4 selectivity, at the expense of a remarkable decrease of Heavy Hydrocarbon production, resulting in enhanced selectivity for the gasoline fraction. In situ XPS experiments show the possible electron transfer from cobalt to carbon and the blockage of metallic cobalt sites, which is responsible for the deactivation of the catalyst. DFT calculations reveal that the activation barrier (Ea) of methane formation decreases by 0.61 eV on the carbon-absorbed Co(111) surface, whereas the Ea of the CH + CH coupling reaction changes unnoticeably. Hydrogenation of CHx to methane becomes the preferable route among the elementary reactions on the Co(111) surface, leading to dramatic changes in the product distribution. Detailed coke-induced deactivation mechanisms of Co-based catalysts during FTS are discussed.Natural Science Foundation of China [21473003, 21222306, 21473229, 91545121, 21273224, 21321002, 21225315]; 973 Project of China [2013CB933100, 2013CB834603]SCI(E)ARTICLE207-22419

R Kandiyoti - One of the best experts on this subject based on the ideXlab platform.

  • Mechanisms of Catalytic Activity in Heavily Coated Hydrocracking Catalysts
    Oil & Gas Science and Technology - Revue d'IFP Energies nouvelles, 2008
    Co-Authors: M. Millan, A A Herod, C. Adell, C. Hinojosa, R Kandiyoti
    Abstract:

    Catalyst deactivation by coke deposition has a direct impact on the economic viability of Heavy Hydrocarbon upgrading processes, such as coal liquefaction and oil residue hydroprocessing. Coke deposition is responsible for rapid loss of catalytic activity and it mostly takes place in the early stages of hydrocracking. The effect of carbonaceous deposition on the catalytic activity of a chromium pillared montmorillonite has been studied in the present work. Its catalytic activity in hydrocracking a coal extract was evaluated based on the boiling point distributions of feed and products obtained by thermogravimetric analysis (TGA), and their characterisation by size exclusion chromatography (SEC) and UV-Fluorescence spectroscopy (UV-F). A large deposition on the catalyst was observed after two successive 2-hour long runs in which the catalyst recovered from the first run was reused in the second. The pillared clay retained its activity even though it showed high carbon loading, a large drop in surface area and complete apparent pore blockage. Some observations may contribute to explain this persistent catalytic activity. First, there is evidence suggesting the dynamic nature of the carbonaceous deposits, which continuously exchange material with the liquid, allowing catalytic activity to continue. Secondly, Scanning Electron Microscopy (SEM) on the used Cr montmorillonite has shown preferential deposition on some regions of the catalyst, which leaves a fraction of the surface relatively exposed. Finally, evidence from SEM coupled to X-ray microanalysis also suggest that deposits are thinner in areas where the active phase of the catalyst is present in higher concentrations. Hydrogenation on the active sites would make the deposits more soluble in the liquid clearing a surrounding area from deposits.

  • effect of catalyst deactivation and reaction time on hydrocracking Heavy Hydrocarbon liquids
    Energy & Fuels, 2007
    Co-Authors: Marcos Millan, Cristina Adell, Cecilia Hinojosa, Alan A Herod, D R Dugwell, R Kandiyoti
    Abstract:

    The activity and fouling behavior of a commercial NiMo/Al2O3 catalyst has been studied during the hydrocracking of a coal extract at short reaction times. The catalyst was precoated with a carbonaceous deposit beforehand in order to study the interaction between a coated catalyst and fresh feed. The conversion of the heavier fraction (boiling point above 450 °C) of the feed steadily increased with time. However, the progression in the amount of carbonaceous deposits on the coated catalyst was not uniform. A large initial deposition was observed when the catalyst and fresh feed were placed in contact. This initial deposition was reversible, and within the first 10 min of reaction, much of the deposit redissolved into the liquid phase with increasing reaction times. This bulk exchange of material between the deposits and the solution appears to be a mechanism which would help explain the sustained level of catalytic activity despite the large carbonaceous deposition. A “harder” more permanent deposit layer ...

  • effect of salts on the sec profiles of Heavy Hydrocarbon liquids new approach with salts dissolved in solvents used for planar chromatography
    Energy & Fuels, 2005
    Co-Authors: Fatma Karaca, Mahtab Behrouzi, Trevor J Morgan, A A Herod, R Kandiyoti
    Abstract:

    Two related propositions addressing the interpretation of size-exclusion chromatograms of Heavy Hydrocarbon liquids have been examined. First, that peaks observed at the exclusion (short retention time) limits of size exclusion chromatography (SEC) columns, when using 1-methyl-2-pyrrolidinone (NMP) as eluent, are due to aggregation brought about by sample polarity. Second, that the addition of salts such as LiBr to the NMP eluent dissipates ionic binding forces and causes the disaggregation of polar clusters. The resulting shift to longer elution times (smaller masses) is then interpreted as representing those of the disaggregated sample molecules. However, in earlier work, we observed that the addition of this salt shifted chromatograms to retention times later than the permeation limits of the analytical columns. The salt appeared to have increased surface interactions between the sample and column packing. Thus, the addition of the salt directly to the SEC eluent did not allow distinguishing between an...

Jae Sung Lee - One of the best experts on this subject based on the ideXlab platform.

  • Carbon dioxide Fischer-Tropsch synthesis: A new path to carbon-neutral fuels
    Applied Catalysis B: Environmental, 2017
    Co-Authors: Yo Han Choi, Young Hye Lee, Sun Hee Choi, Hunmin Park, Won Young Kim, Youn Jeong Jang, Jae Sung Lee
    Abstract:

    Paradigm of climate change mitigation technologies is shifting from carbon capture and storage (CCS) to carbon capture and utilization (CCU). Here we propose a new path to CCU – direct CO2 conversion to liquid transportation fuels by reacting with renewable hydrogen produced by solar water splitting. The highly promising and CO2-neutral CCU system is possible by our discovery of a new catalyst that produces liquid Hydrocarbon (C5+) selectivity of ∼65% and greatly suppressed CH4 formation to 2–3%, which represents an unprecedented selectivity pattern for direct catalytic CO2 hydrogenation and is very similar to that of conventional CO-based Fischer-Tropsch (FT) synthesis. The catalyst was prepared by reduction of delafossite-CuFeO2 and in-situ carburization to Hägg carbide (χ-Fe5C2), the active phase for Heavy Hydrocarbon formation. The reference catalysts derived from bare Fe2O3, CuO-Fe2O3 mixture, and spinel CuFe2O4 are much less active and produce mainly light Hydrocarbons, highlighting the critical role of delafossite-CuFeO2 as the catalyst precursor. The new catalyst breaks through the limitation of CO2-based FT synthesis and will open the avenue for new opportunity for carbon recycling into valuable liquid fuels at the similar conditions to industrially practiced CO-FT synthesis.

Daniel F Smith - One of the best experts on this subject based on the ideXlab platform.

  • bio fuel reformation for solid oxide fuel cell applications part 1 fuel vaporization and reactant mixing
    International Journal of Hydrogen Energy, 2013
    Co-Authors: Thomas A Trabold, Mark R Walluk, Daniel F Smith
    Abstract:

    Abstract A new configuration of a mixing chamber integrated with a customized porous nozzle has been developed to completely vaporize Heavy Hydrocarbon fuels (e.g., diesel, biodiesel) and achieve homogenous mixing of fuel/air/steam. This proposed configuration suppresses Hydrocarbon thermal pyrolysis and solid carbon formation in the fuel vaporization step. The porous nozzle promotes the micro-explosion of emulsified fuel and accelerates secondary atomization to reduce the droplet size. The mixing chamber with customized nozzle was integrated in a single-tube reformer system in order to analyze its effect on diesel and biodiesel auto-thermal reforming (ATR). It has been demonstrated that the customized nozzle not only improved the hydrogen production rate and the reforming efficiency, but it also stabilized the chemical reactions within the reformer and prevented the reactor inlet from high temperature sintering. For diesel ATR, this mixing chamber–reformer combination enabled operation at relatively low reformer temperature without forming solid carbon. This study is one component of a three-part investigation of bio-fuel reforming, also including biodiesel (Part 2) and biodiesel–diesel blends (Part 3).

Yuesong Shen - One of the best experts on this subject based on the ideXlab platform.

  • small scale reforming of diesel and jet fuels to make hydrogen and syngas for fuel cells a review
    Applied Energy, 2013
    Co-Authors: Xinhai Xu, Peiwen Li, Yuesong Shen
    Abstract:

    This paper reviews the technological features and challenges of autothermal reforming (ATR) of Heavy Hydrocarbon fuels for producing hydrogen and syngas onboard to supply fuels to fuel cells for auxiliary power units. A brief introduction at the beginning enumerates the advantages of using Heavy Hydrocarbon fuels onboard to provide hydrogen or syngas for fuel cells such as solid oxide fuel cells (SOFCs). A detailed review of the reforming and processing technologies of diesel and jet fuels is then presented. The advantages of ATR over steam reforming (SR) and partial oxidation reforming (POX) are summarized, and the ATR reaction is analyzed from a thermodynamic point of view. The causes and possible solutions to the major problems existing in ATR reactors, including hot spots, formation of coke, and inhomogeneous mixing of fuel, steam, and air, are reviewed and studied. Designs of ATR reactors are discussed, and three different reactors, one with a fixed bed, one with monoliths, and one with microchannels are investigated. Novel ideas for design and startup strategies for ATR reactors are proposed at the end of the review.