Three inter-linked active sites in the dehydrogenation of n-octane over magnesium molybdate based catalysts and their influences on coking and cracking side reactions

Fadlalla, Mohamed I.; Farahani, Majid D.; Friedrich, Holger B.

doi:10.1016/j.mcat.2018.10.006

Cited by 16 publications

(5 citation statements)

References 43 publications

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“…The activation of n-octane at 450 °C, using the 0.04 mol alkaline earth metal modified Ga-NaY catalysts showed the previously reported ODH products of n-octane, which were octenes, aromatics, oxygenates, cracked products and carbon oxides [1][2][3][4]. Only GHSV was varied between the catalysts to achieve iso-conversion.…”

Section: Product Selectivity At Iso-conversionmentioning

confidence: 52%

“…Oxidation, cracking, dehydrogenation, dehydrocyclization, and oxidative dehydrogenation are possible reactions that can activate paraffins using heterogeneous catalysts. Dehydrogenation (DH) of n-octane is one of the important reactions industrially and can be carried out using a variety of catalysts, both mono-and bi-functional [1][2][3][4]. Paraffins are easily and cheaply obtained from natural gas and petroleum, and this, with their relative environmental friendliness, makes them interesting alternatives to olefinic and aromatic feedstocks.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Modifying Acidity and Reducibility on the Activity of NaY Zeolite in the Oxidative Dehydrogenation of n-Octane

2020

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Non-coking stable alkaline earth metal (M = Mg, Sr, and Ba) modified Ga-NaY catalysts were prepared by ionic-exchange and tested in oxidative dehydrogenation (ODH) of n-octane using air as the source of oxygen. The role of the alkaline earth metals in NaY was to poison the acid sites while enhancing the basic sites responsible for ODH. The exception was the calcium modified NaY, which was more acidic than the parent NaY, coking and unstable under the ODH conditions used in this study. The role of gallium was to enhance the dehydrogenation pathway and improve the stability of NaY. The sequence of increasing selectivity to octenes followed the order: CaGa-NaY < Ga-NaY< MgGa-NaY < SrGa-NaY < BaGa-NaY. The highest octene selectivity obtained was 37% at iso-conversion of 6 ± 1% when BaGa-NaY was used at a temperature of 450 °C. The activity of the catalysts was directly proportional to the reducibility of the catalysts, which is in agreement with expectations.

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Section: Product Selectivity At Iso-conversionmentioning

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Effects of Modifying Acidity and Reducibility on the Activity of NaY Zeolite in the Oxidative Dehydrogenation of n-Octane

2020

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“…The catalyst which was determined to have the lowest nickel occupation in both these sites (Sp-0.06 Nb) and less oxygen vacancies from XPS data showed the highest selectivity to carbon oxides. Fadalla et al [58] again reported the oxidative dehydrogenation of n-octane over molybdate-based catalysts. This study focused on the application of magnesium molybdate with different Mg:Mo ratios ranging from 1:0.87 to 1:1.25.…”

Section: Unsupported Metal Oxidesmentioning

confidence: 97%

“…It has been shown that the formation of active oxygen species during the re-oxidation of the catalysts influences the selectivity of products in the oxidative dehydrogenation of n-octane. Mechanistic investigations have revealed that the basicity and the redox capacity of the metal will influence the selectivity to olefins [55,58]. Metal oxides interact with the hydrogen atoms of alkanes and promote the dissociation of C-H bonds and the subsequent formation of hydrogen and olefins.…”

Section: Catalysts Usedmentioning

confidence: 99%

Gas-Phase Oxidative Dehydrogenation of n-Octane over Metal Oxide Catalysts: A Review

Ntola,

Shozi

2024

Catalysts

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The oxidative dehydrogenation (ODH) of alkanes, whereby hydrogen is removed to form unsaturated compounds, is an important process, particularly in the petrochemical industry. The ODH of lighter alkanes (C3–C6) is well-reported in the literature, and while there are several reports on the ODH of n-octane (C8), there is no reported review of the important findings in the literature. This review discusses the gas-phase ODH of n-octane occurring at high temperatures (300–550 °C). The mechanisms via which the n-octane ODH of occurs are also briefly discussed. The oxidants (mainly O2 and CO2) and catalysts (supported and unsupported metal oxides) are discussed as well as the effect of these and the temperature on the type of products formed and their various distributions. Furthermore, the review looks at the acid–base and redox properties of the catalysts and how they affect product formation. Some challenges as well as perspectives of the ODH process are also highlighted.

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“…In addition, a large number of coking precursors formed in combustion also restrict the efficient utilization of a transport fuel. , Accurate prediction of the difference in coke precursor formation is of great help to evaluate the coking trend of isomer fuels. − However, a comprehensive introduction to the coking mechanism difference of six isomers is rarely reported in the literature . Most of them only introduce the coking behavior of individual isomers, for example, Friedrich et al found that the addition of a metal (Mg) would promote the undesired coking reactions of n -octane. Therefore, an in-depth understanding of the coking mechanism difference of octane isomers is of significance to improve fuel quality and provide a reliable basis for selecting suitable fuel surrogates.…”

Section: Introductionmentioning

confidence: 99%

ReaxFF MD Investigation of the High-Temperature Combustion of Six Octane Isomers

et al. 2021

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This work attempts to investigate the combustion mechanism, reactivity, and coking performance of six octane isomers using reactive molecular dynamics (ReaxFF MD) simulations and the VARxMD code. The kinetic analysis results were firstcompared with the experimental data to verify the validity of the simulation results. It was found that the combustion of six isomers mainly involves C−C bond cleavage, isomerization reactions, dehydrogenation, and oxidation. The cleavage of C−C bonds is the dominant route of initial reactions in combustion. While the isomerization reaction is a major distinction between normal and branched alkane isomers. The formation mechanism of coke precursors was further discussed by pathway analysis. The results showed that the existence of branch chains increases the possibility of the formation of coking precursors, and monoethyl isomers show the highest generation trend. The methyl substitution location also has an obvious effect on the formation mechanism of coke precursors. For meta-methyl isomers, coke precursors are formed by dehydrogenation of macromolecules at high temperature, while those are caused by collisions between carbon atoms for ortho-methyl isomers. The product distribution showed that the number of ethylene groups in n-octane combustion is larger than that of other isomer systems, while there is more CO formed in 2,2,3,3-tetramethylbutane combustion. For reactivity, the n-alkane is more reactive than other isomer systems, and increasing the number of methyl substitutions also enhances the reactivity of branched isomers for multimethyl isomers. Hopefully, the mechanism information obtained in this work could improve the understanding of differences in combustion of octane isomers and provide insights into the structural effect during the fuel combustion process at the molecular level.

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Three inter-linked active sites in the dehydrogenation of n-octane over magnesium molybdate based catalysts and their influences on coking and cracking side reactions

Cited by 16 publications

References 43 publications

Effects of Modifying Acidity and Reducibility on the Activity of NaY Zeolite in the Oxidative Dehydrogenation of n-Octane

Effects of Modifying Acidity and Reducibility on the Activity of NaY Zeolite in the Oxidative Dehydrogenation of n-Octane

Gas-Phase Oxidative Dehydrogenation of n-Octane over Metal Oxide Catalysts: A Review

ReaxFF MD Investigation of the High-Temperature Combustion of Six Octane Isomers

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