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Hongwei Xiang - One of the best experts on this subject based on the ideXlab platform.

  • Study of phase transformation and catalytic performance on precipitated Iron-Based Catalyst for Fischer–Tropsch synthesis
    Journal of Molecular Catalysis A-chemical, 2009
    Co-Authors: Mingyue Ding, Chenghua Zhang, Yong Yang, Hongwei Xiang
    Abstract:

    Abstract Detailed phase transformation in syngas (H2/CO = 1.2) on a precipitated Iron-Based Catalyst was studied by N2 physisorption, X-ray diffraction (XRD), Mossbauer effect spectroscopy (MES), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (LRS). Fischer–Tropsch synthesis (FTS) performance of the Catalyst was investigated in a slurry-phase continuously stirred tank reactor (STSR). The hematite in the fresh Catalyst was reduced initially to magnetite, and then the magnetite in the bulk reached steady state slowly with increasing reduction time. Simultaneously, the Fe3O4 on the surface layers converted gradually to iron carbides, accompanied with the continual increase in the amounts of surface carbonaceous species. In the FTS reaction, the catalytic activity presented an increased trend with gradual carburization of the Catalyst by keeping the stability in the bulk Fe3O4, suggesting that the conversion of magnetite to iron carbides in the near-surface regions provides probably the active sites for FTS. In addition, the chain growth reaction was restrained and the hydrogenation reaction was enhanced with increasing reduction duration.

  • Activation pressure studies with an Iron-Based Catalyst for slurry Fischer-Tropsch synthesis
    Journal of Natural Gas Chemistry, 2009
    Co-Authors: Qinglan Hao, Liang Bai, Hongwei Xiang
    Abstract:

    Abstract Fischer-Tropsch synthesis (FTS) was carried out with an industrial Iron-Based Catalyst (100Fe/5Cu/6K/16SiO 2 , by weight) under the baseline conditions in a stirred tank slurry reactor (STSR). The effects of activation pressure on the Catalyst activity and selectivity were investigated. It was found that iron phase compositions, textural properties, and FTS performances of the Catalysts were strongly dependent on activation pressure. The high activation pressure retards the carburization. Mossbauer effect spectroscopy (MES) results indicated that the contents of the iron carbides clearly decrease with the increase of activation pressure, especially for the activation pressure increasing from 1.0 MPa to 1.5 MPa, and the reverse trend is observed for superparamagnetic Fe 3+ (spm). The higher content of Fe 3+ (spm) results in the higher amount of CO 2 in tail gas when the Catalyst is reduced at higher pressure. The Catalyst activity decreases with the increase of activation pressure. The high quantity of iron carbides is necessary to obtain high FTS activity. However, the activity of the Catalyst activated in syngas can not be predicted solely from the fraction of the carbides. It is concluded that activation with syngas at the lower pressure would be the most desirable for the better activity and stability on the Iron-Based Catalyst.

  • Promotional effects of Cu and K on precipitated Iron-Based Catalysts for Fischer–Tropsch synthesis
    Journal of Molecular Catalysis A: Chemical, 2008
    Co-Authors: Haijun Wan, Chenghua Zhang, Hongwei Xiang
    Abstract:

    The effects of Cu and K promoters on precipitated Iron-Based Fischer-Tropsch synthesis (FTS) Catalysts were investigated by using N-2 physical adsorption, temperature-programmed reduction/desorption (TPR/TPD) and Mossbauer effect spectroscopy (MES). The FTS performances of the Catalysts were tested in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that Cu promoter facilitates the high dispersion of Fe2O3, significantly promotes the reduction and H-2 adsorption, but severely suppresses CO adsorption and the carburization. However, K promoter severely retards the reduction and suppresses the H-2 adsorption, facilitates the CO adsorption and promotes the carburization. In the FTS reaction, it was found that Cu promoter decreases the FFS initial activity and water gas shift (WGS) reaction activity, promotes the oxidation of iron carbides to Fe3O4 and accelerates the deactivation of Iron-Based Catalyst. However, K promoter improves the FTS activity and WGS reaction activity, suppresses the oxidation of iron carbide to Fe3O4 and significantly improves the stability of Iron-Based Catalyst. As compared with individual promotion of Cu or K, the double promotions of Cu and K significantly improve the FTS and WGS activities and keep excellent stability. Due to weaker CO adsorption and stronger H-2 adsorption than the Catalysts without Cu, Cu promoted Catalysts have higher selectivity to light hydrocarbons and methane and lower selectivity to heavy hydrocarbons. However, the opposite result is obtained on the Catalyst incorporated with K promoter

  • Promotional effects of Cu and K on precipitated Iron-Based Catalysts for Fischer-Tropsch synthesis
    Journal of Molecular Catalysis A-chemical, 2007
    Co-Authors: Haijun Wan, Chenghua Zhang, Hongwei Xiang
    Abstract:

    The effects of Cu and K promoters on precipitated Iron-Based Fischer-Tropsch synthesis (FTS) Catalysts were investigated by using N-2 physical adsorption, temperature-programmed reduction/desorption (TPR/TPD) and Mossbauer effect spectroscopy (MES). The FTS performances of the Catalysts were tested in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that Cu promoter facilitates the high dispersion of Fe2O3, significantly promotes the reduction and H-2 adsorption, but severely suppresses CO adsorption and the carburization. However, K promoter severely retards the reduction and suppresses the H-2 adsorption, facilitates the CO adsorption and promotes the carburization. In the FTS reaction, it was found that Cu promoter decreases the FFS initial activity and water gas shift (WGS) reaction activity, promotes the oxidation of iron carbides to Fe3O4 and accelerates the deactivation of Iron-Based Catalyst. However, K promoter improves the FTS activity and WGS reaction activity, suppresses the oxidation of iron carbide to Fe3O4 and significantly improves the stability of Iron-Based Catalyst. As compared with individual promotion of Cu or K, the double promotions of Cu and K significantly improve the FTS and WGS activities and keep excellent stability. Due to weaker CO adsorption and stronger H-2 adsorption than the Catalysts without Cu, Cu promoted Catalysts have higher selectivity to light hydrocarbons and methane and lower selectivity to heavy hydrocarbons. However, the opposite result is obtained on the Catalyst incorporated with K promoter.

  • Study of Manganese Promoter on a Precipitated Iron-Based Catalyst for Fischer-Tropsch Synthesis
    Journal of Natural Gas Chemistry, 2007
    Co-Authors: Yong Yang, Tingzhen Li, Hongwei Xiang, Chenghua Zhang, Mingyue Ding, Yong-wang Li
    Abstract:

    Abstract The effects of Manganese (Mn) incorporation on a precipitated Iron-Based Fischer-Tropsch synthesis (FTS) Catalyst were investigated using N2 physical adsorption, air differential thermal analysis (DTA), H2 temperature-programmed reduction (TPR), and Mossbauer spectroscopy. The FTS performances of the Catalysts were tested in a slurry phase reactor. The characterization results indicated that Mn increased the surface area of the Catalyst, and improved the dispersion of α-Fe2O3 and reduced its crystallite size as a result of the high dispersion effect of Mn and the Fe-Mn interaction. The Fe-Mn interaction also suppressed the reduction of α-Fe2O3 to Fe3O4, stabilized the FeO phase, and (or) decreased the carburization degree of the Catalysts in the H2 and syngas reduction processes. In addition, incorporated Mn decreased the initial Catalyst activity, but improved the Catalyst stability because Mn restrained the reoxidation of iron carbides to Fe3O4, and improved further carburization of the Catalysts. Manganese suppressed the formation of CH4 and increased the selectivity to light olefins (C=2–4), but it had little effect on the selectivities to heavy (C5+) hydrocarbons. All these results indicated that the strong Fe-Mn interaction suppressed the chemisorptive effect of the Mn as an electronic promoter, to some extent, in the precipitated iron-manganese Catalyst system.

Christophe Darcel - One of the best experts on this subject based on the ideXlab platform.

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

Luis C Misal Castro - One of the best experts on this subject based on the ideXlab platform.

Qi Wang - One of the best experts on this subject based on the ideXlab platform.

  • Synthesis of polyethylene with bimodal molecular weight distribution by supported iron‐based Catalyst
    Journal of Polymer Science Part A: Polymer Chemistry, 2004
    Co-Authors: Qi Wang
    Abstract:

    Through immobilization of two Iron-Based complexes, [((2,6-MePh)N = C(Me))2C5H3N]FeCl2 (1) and [((2,6-iPrPh)N = C(Me))2C5H3N]FeCl2 (2), on SiO2 pretreated with tetraethylaluminoxane (TEAO), two supported Iron-Based Catalysts, 1/TEAO/SiO2 (3) and 2/TEAO/SiO2 (4), were prepared. These two supported Catalysts 3 and 4 could be used to catalyze ethylene polymerization with moderate polymerization activity and prepare linear high-density polyethylene with bimodal molecular weight distribution (MWD). It was demonstrated that immobilization of Catalyst could significantly improve molecular weight (MW) of high-MW fraction of the resultant polyethylene, as well as maintain bimodal MWD of polyethylene produced by the corresponding homogeneous Catalysts. Such bimodal MWD of polyethylene produced by supported Iron-Based Catalysts could be well tailored by varying polymerization conditions, such as ethylene pressure and molar ratio of Al to Fe. It has been proven that TEAO is an efficient activator for both homogeneous and heterogeneous Iron-Based Catalysts for producing polyethylene with bimodal MWD. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5662–5669, 2004

  • Effect of aluminoxane on molecular weight and molecular weight distribution of polyethylene prepared by an Iron-Based Catalyst
    Polymer International, 2004
    Co-Authors: Qi Wang
    Abstract:

    A series of aluminoxanes, tetraethylaluminoxane (TEAO), tetraalkylaluminoxane (TAAO), Et2AlOB(4 − F − C6H4)OAlEt2 (BTEAO) and ethyl-iso-butylaluminoxane modified with p-fluorophenylboric acid (BEBAO), were prepared and their effects on molecular weight (MW) and molecular weight distribution (MWD) of polyethylene prepared by the Iron-Based Catalyst [(ArNC(Me))2C5H3N]FeCl2 (Ar2,6-dimethylphenyl) (1) were investigated. It was found that TEAO and BTEAO were highly efficient activators for Iron-Based Catalysts and introducing the branched bulky group (eg iso-Bu) into the aluminoxane activator could improve the MW of the resulting polyethylene. The MW of polyethylene produced by activators modified by p-fluorophenylboric acid was higher than for other aluminoxane activators. The TEAO- and TAAO-based polyethylene exhibited attractive bimodal MWD, and the lower MW fraction of bimodal MWD was shown to be produced in the early stage of polymerization due to chain transfer to the aluminium activator. Copyright © 2004 Society of Chemical Industry