The Optimally Performing Fischer–Tropsch Catalyst

Filot, Ivo A. W.; Santen, Rutger A. van; Hensen, Emiel J. M.

doi:10.1002/ange.201406521

Cited by 61 publications

(62 citation statements)

References 53 publications

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“…We already showed that the FT reaction has several kinetic regimes and the Rucatalyzed FT reaction operates in a kinetic regime, where CO dissociation is not controlling the overall rate. 23 This is supported by the results in Figure 5, where it can be seen that the surface stability of CO does not influence the chain-growth probability. The interesting consequence is that, when CO dissociation is not rate-controlling, an increase in the number of free surface sites does not necessarily increase the overall CO consumption rate and the chain-growth probability.…”

Section: Resultssupporting

confidence: 79%

Kinetic aspects of chain growth in Fischer–Tropsch synthesis

et al. 2017

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Microkinetics simulations are used to investigate the elementary reaction steps that control chain growth in the Fischer-Tropsch reaction. Chain growth in the FT reaction on stepped Ru surfaces proceeds via coupling of CH and CR surface intermediates. Essential to the growth mechanism are C-H dehydrogenation and C hydrogenation steps, whose kinetic consequences have been examined by formulating two novel kinetic concepts, the degree of chain-growth probability control and the thermodynamic degree of chain-growth probability control. For Ru the CO conversion rate is controlled by the removal of O atoms from the catalytic surface. The temperature of maximum CO conversion rate is higher than the temperature to obtain maximum chain-growth probability. Both maxima are determined by Sabatier behavior, but the steps that control chain-growth probability are different from those that control the overall rate. Below the optimum for obtaining long hydrocarbon chains, the reaction is limited by the high total surface coverage: in the absence of sufficient vacancies the CHCHR → CCHR + H reaction is slowed down. Beyond the optimum in chain-growth probability, CHCR + H → CHCHR and OH + H → H 2 O limit the chain-growth process. The thermodynamic degree of chain-growth probability control emphasizes the critical role of the H and free-site coverage and shows that at high temperature chain depolymerization contributes to the decreased chain-growth probability. That is to say, during the FT reaction chain growth is much faster than chain depolymerization, which ensures high chain-growth probability. The chain-growth rate is also fast compared to chain-growth termination and compared to the steps that control the overall CO conversion rate, which are O removal steps for Ru.

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Section: Resultssupporting

confidence: 79%

Kinetic aspects of chain growth in Fischer–Tropsch synthesis

et al. 2017

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“…Energy reference is CO and H 2 in gas phase. 110 CH-CH recombination is lower than the overall activation barrier for CHC formation via CO insertion because of the high C-O bond cleavage activation energy. Hence the carbide chain growth mechanism will dominate.…”

Section: In Summarymentioning

confidence: 98%

“…The reaction is endothermic by 60 kJ mol À1 . On the open Ru surface, Filot et al 110 report activation energy of the CO with ''CH'' reaction to be 60 kJ mol À1 , which is 30 kJ mol À1 endothermic. The effective rate constant for chain growth termination though requires at least one additional hydrogen addition step (see Fig.…”

Section: C-c Bond Formation and Chain Terminationmentioning

confidence: 99%

Mechanism and microkinetics of the Fischer–Tropsch reaction

Santen

Markvoort

Filot

et al. 2013

Phys. Chem. Chem. Phys.

243

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The increasing availability of quantum-chemical data on surface reaction intermediates invites one to revisit unresolved mechanistic issues in heterogeneous catalysis. One such issue of particular current interest is the molecular basis of the Fischer-Tropsch reaction. Here we review current molecular understanding of this reaction that converts synthesis gas into longer hydrocarbons where we especially elucidate recent progress due to the contributions of computational catalysis. This perspective highlights the theoretical approach to heterogeneous catalysis that aims for kinetic prediction from quantum-chemical first principle data. Discussion of the Fischer-Tropsch reaction from this point of view is interesting because of the several mechanistic options available for this reaction. There are many proposals on the nature of the monomeric single C atom containing intermediate that is inserted into the growing hydrocarbon chain as well as on the nature of the growing hydrocarbon chain itself. Two dominant conflicting mechanistic proposals of the Fischer-Tropsch reaction that will be especially compared are the carbide mechanism and the CO insertion mechanism, which involve cleavage of the C-O bond of CO before incorporation of a CHx species into the growing hydrocarbon chain (the carbide mechanism) or after incorporation into the growing hydrocarbon chain (the CO insertion mechanism). The choice of a particular mechanism has important kinetic consequences. Since it is based on molecular information it also affects the structure sensitivity of this particular reaction and hence influences the choice of catalyst composition. We will show how quantum-chemical information on the relative stability of relevant reaction intermediates and estimates of the rate constants of corresponding elementary surface reactions provides a firm foundation to the kinetic analysis of such reactions and allows one to discriminate between the different mechanistic options. The paper will be concluded with a short perspective section dealing with the needs for future research. Many of the current key questions on the physical chemistry as well as computational study of heterogeneous catalysis relate to particular topics for further research on the fundamental aspects of Fischer-Tropsch catalysis.

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“…Experimental approaches using model catalysts, co-feeding studies or transient techniques have been used to obtain insights into mechanistic details of the Fischer-Tropsch chain growth reaction [18][19][20][21]. More recently, theoretical calculations using ideal surface structures have been used to study the mechanism on the molecular level [8,22,23]. The experimental counterpart of this, surface science using single crystal surfaces, has rarely been employed for the cobalt system, although there are many opportunities for decisive studies on relevant elementary steps in the mechanism, particularly if such experiments are complemented by state-of-the-art computational studies [24].…”

Section: Introductionmentioning

confidence: 99%