The mechanism and kinetics study of Fischer‒Tropsch reaction over iron-nickel-cerium nano-structure catalyst

https://doi.org/10.1016/j.ijhydene.2019.07.222Get rights and content

Highlights

  • The mechanism and kinetics of FT reaction were studied using Fe–Ni–Ce catalyst.

  • The rate equations of CO consumption were obtained based on proposed mechanisms.

  • The best kinetic model was chosen by non-linear regression analysis.

  • The kinetic parameters including Ea and ΔHads were estimated.

  • The nanocatalyst was characterized by XRD, FESEM, and BET methods.

Abstract

The kinetic of Fischer‒Tropsch reaction was investigated using the iron‒nickel‒cerium nano-structure catalyst synthesized by the hydrothermal method in the fixed-bed micro reactor for the first time. The kinetic tests carried out under operating conditions including the pressure of 2–10 bar, temperature of 230–250 °C, molar ratio H2/CO of 1, and the gas space velocity of 3000 h−1. Twenty-two set of reaction mechanisms were proposed on the basis of the adsorption nature of carbon monoxide, and hydrogen using the Langmuir‒Hinshelwood‒Hougen‒Watson, and Eley Rideal adsorption theories for the FT reaction. The rate equations of CO consumption were obtained based on the proposed reaction mechanisms. The best kinetic model was chosen by non-linear regression analysis and its kinetic parameters including activation energy, adsorption enthalpies of H2, and CO were estimated 60.4, −3.24, and −65.7 kJ/mol respectively. The nanocatalyst was characterized by various techniques such as XRD, FESEM, and Brunauer–Emmett–Teller surface area measurements.

Introduction

The Fischer‒Tropsch (FT) reaction is an alternative non-oil route for the production of a wide range of hydrocarbons including chemical and clean fuels from synthesis gas (H2 and CO). The FT technology had received much attention as a key part of the gas to liquids (GTL) process in the academic or industrial topic due to the decrease of oil reserves and increase of the oil in recent decades. The FT products are as environmentally synthetic fuel have low contents of sulfur, nitrogen, and aromatics [1], [2], [3].

The choice of catalyst components plays a major role in the catalytic activity and products selectivity. The transition metals including Fe, Co, Ni, and Ru are common as key components of the FT catalysts. Iron-based catalysts are a reasonable choice due to low cost, high water-gas shift (WGS) reactivity, and particularly applicable for synthesis gas with the low H2/CO ratio for the conversion of syngas [4], [5]. Nickel exhibits diverse catalytic manner. The molecular mass of the gained hydrocarbons using nickel catalysts is much lower compared to iron and cobalt catalysts. Thus, the appending of Ni to Fe or Co catalysts could lead to enhancement of light olefins content in the products [6], [7]. Perez-Alonso et al. claimed that cerium link with iron improves the catalyst performance. The addition of cerium to catalyst raised the rate of reverse WGS reaction by hydrogenation of carbon dioxide and the production of CO and also minimizes carbon deposition during the FT synthesis [8], [9]. It is approved that the combination of metal components improves the activity and stability of the catalyst compared to the one or two component catalysts due to the possible electronic interaction between metal species [10], [11], [12].

Kinetics modeling and mechanism description are two key factors in the optimization, simulation, and process design in the commercial scale. The FT synthesis is the surface polymerization reaction including the following steps: reactants adsorption (CO and H2), chain formation, chain propagation, chain termination, and products desorption [13]. The detailed mechanism is very complicated because of the various elementary reaction steps and the great number of species so that was not still perceived completely [14], [15]. Methylene formation is considered as the rate determining step because it is a very low step in comparison with chain propagation and products desorption [16], [17].

Kinetics of FT reaction can be divided into two categories [18], [19], [20], [21]. At first approach, the reaction rate equations are expressed based on the consumption of reactants (carbon monoxide and hydrogen) using the FT reaction mechanism and lumped kinetic models. The second is described on the basis of the product distribution due to the propagation and growth of hydrocarbons chain. The kinetics of the FT reaction has investigated through the first method by many researchers and the rate expressions have been presented in the three types including power law, Langmuir-Hinshelwood-Hougen-Watson (LHHW), and Eley Rideal (ER) theories. The most rate expressions have been extended by fitting the data to the power law type that the model is the follows:rCO=k(PCO)a(PH2)b

It is accepted that value of (a) was from +0.65 to −1 and value of (b) was from 0.5 to 2 [22], [23]. Many researchers applied LHHW, and ER type mechanisms to attain the rate expressions. In the LHHW adsorption theory, the reactants adsorbed on the catalyst surface and reaction occurred between surface adsorbed species whereas the ER model illustrates the reaction ocurred between gaseous species. The reaction rate equation was written based on the rate determining step and expressed as a function of gas species pressure as regards:rCO=kPCOPH2a(1+kibi)b(i=CO,H2,H2O, andCO2)k is the equilibrium constant in the rate expression.

The kinetics of the FT reaction has been studied using the single and bimetallic catalysts, such as Fe–Ni and Fe–Ce [17], [24], [25], [26]. Mirzaei et al. were investigated the kinetics and mechanism of the FT reaction using the three metallic catalysts for the first time [10], [27], [28], [29]. In the previous our work, the three metallic Fe‒Ni‒Ce nanocatalyst was prepared by the hydrothermal method in the presence of polyethylene glycol. The products selectivity and catalytic activity were investigated at different preparation and operating conditions [30]. In the present research, the kinetic and mechanism of FT reaction were studied over the Fe‒Ni‒Ce nanocatalyst based on LHHW rate equations. The kinetic model and its parameters were obtained using the nonlinear regression analysis. The catalyst characterization was performed by various techniques such as XRD, FE-SEM, and BET method. Finally, the obtained results were compared to the previously reported results.

Section snippets

Nanocatalyst synthesis

The iron‒nickel‒cerium nanocatalyst was prepared by the hydrothermal method. In a typical procedure, specified amounts of Fe (NO3)3 .9H2O, Ni (NO3)2 .6H2O, and Ce (NO3)3 .6H2O with 99.9% purity Merck were dissolved separately in the deionized water. The solutions were combined together and stirred at the room temperature. Then, the NaOH solution was added dropped to the solution and subsequently a certain amount of polyethylene glycol (PEG 600) as the surfactant was added to the solution. After

Catalyst characterization

The XRD technique used to identify the crystal structure and the actual phases of the iron‒nickel‒cerium ternary nanocatalyst prepared by hydrothermal method. The XRD pattern of the nanocatalyst have indicated in Fig. 2. As can be seen, the diffraction peaks are sharp and strong in the XRD pattern that demonstrate the appropriate crystallization of the nanocatalyst. The main phases of the fresh nanocatalysts before the FT reaction are the NiFe2O4 (cubic), Fe2O3 (tetragonal), Fe2O3

Conclusion

The kinetic of FT reaction was investigated using an iron‒nickel‒cerium nanocatalyst under a range of operating conditions including the pressure of 2–10 bar, temperature of 230–250 °C, molar ratio H2/CO of 1/1, and GHSV of 3000 h−1 in a fixed-bed reactor. The iron‒nickel‒cerium ternary nanocatalyst was prepared by the hydrothermal method and was characterized by XRD, FESEM, EDS, and BET surface area measurements methods. Twenty-two set of reaction mechanisms were described on the basis of the

Acknowledgements

The authors would like to appreciate the financial supports of this research project at the university of Sistan and Baluchestan and the Ministry of Science.

References (53)

  • T.J. Okeson et al.

    On the kinetics and mechanism of Fischer–Tropsch synthesis on a highly active iron catalyst supported on silica-stabilized alumina

    Catal Today

    (2016)
  • M. Sarkari et al.

    Fischer–Tropsch synthesis: development of kinetic expression for a sol–gel Fe–Ni/Al2O3 catalyst

    Fuel Process Technol

    (2012)
  • A.A. Mirzaei et al.

    Kinetic study of CO hydrogenation over co-precipitated iron–nickel catalyst

    J Ind Eng Chem

    (2012)
  • A.A. Mirzaei et al.

    Kinetics modeling of Fischer‒Tropsch synthesis on the unsupported Fe-Co-Ni (ternary) catalyst prepared using co-precipitation procedure

    Fuel

    (2015)
  • M. Abbasi et al.

    Hydrothermal synthesis of Fe-Ni-Ce nano-structure catalyst for Fischer-Tropsch synthesis: characterization and catalytic performance

    J Alloy Comp

    (2019)
  • S. Storsaeter et al.

    Study of the effect of water on Fischer–Tropsch synthesis over supported cobalt catalysts

    J Catal

    (2005)
  • R. Zennaro et al.

    Kinetics of Fischer–Tropsch synthesis on titania-supported cobalt

    Catal Today

    (2000)
  • H.B. Zhang et al.

    Characterization of a fused iron catalyst for FischerTropsch synthesis by in situ laser Raman spectroscopy

    J Catal

    (1985)
  • M.D. Shroff et al.

    Activation of precipitated Iron Fischer-Tropsch synthesis catalysts

    J Catal

    (1995)
  • J.S. Kim et al.

    Performance of catalytic reactors for the hydrogenation of CO2 to hydrocarbons

    Catal Today

    (2006)
  • T. Li et al.

    Study on an iron–nickel bimetallic Fischer–Tropsch synthesis catalyst

    Fuel Process Technol

    (2014)
  • G.P. Van der Laan et al.

    Intrinsic kinetics of the gas–solid Fischer–Tropsch and water gas shift reactions over a precipitated iron catalyst

    Appl Catal

    (2000)
  • S. Mousavi et al.

    Generalized kinetic model for iron and cobalt based Fischer-Tropsch synthesis catalysts: review and model evaluation

    Appl Catal A

    (2015)
  • H. Atashi et al.

    Kinetic study of Fischer-Tropsch process on titania-supported cobalt-manganese catalyst

    J Ind Eng Chem

    (2010)
  • Y.N. Wang et al.

    Kinetics modelling of Fischer-Tropsch synthesis over an industrial Fe–Cu–K catalyst

    Fuel

    (2003)
  • F. Fazlollahi et al.

    Preparation of Fe-Mn/K/Al2O3 Fischer-Tropsch catalyst and its catalytic kinetics for the hydrogenation of carbon monoxide

    Chin J Chem Eng

    (2013)
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