Redox properties and catalytic performance of complex oxides in oxidative coupling of methane

Sinev, M. Yu.; Bychkov, V. Yu.; Корчак, В. Н.; Tulenin, Yu. P.; Fattakhova, Z. T.; Калашникова, О. В.

doi:10.1016/0920-5861(94)80158-4

Cited by 2 publications

(4 citation statements)

References 11 publications

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“…The key role of surface hydroxyl groups was discussed, while a kinetic model accounting for surface interactions and diffusion of oxygen, hydrogen, and hydroxyl ions in the oxide lattice was developed to account for the participation of lattice oxygen in methane oxidation. 19 More recently, the author's findings were consolidated in an elaborate microkinetic model that was able to describe qualitatively various experimental observations. 20,21 In the work of Couwenberg et al, 22 it was established that the participating gas-phase intermediates are highly reactive and lead to irreducible mass transport limitations for the latter.…”

Section: Introductionmentioning

confidence: 97%

“…Early on, the interaction of radicals with the surface was investigated, , wherein a Polanyi correlation was applied to determine the activation energies of the various proposed heterogeneous steps by postulating an analogy with equivalent homogeneous steps. The key role of surface hydroxyl groups was discussed, while a kinetic model accounting for surface interactions and diffusion of oxygen, hydrogen, and hydroxyl ions in the oxide lattice was developed to account for the participation of lattice oxygen in methane oxidation . More recently, the author’s findings were consolidated in an elaborate microkinetic model that was able to describe qualitatively various experimental observations. , …”

Section: Introductionmentioning

confidence: 99%

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Oxidative Coupling of Methane: A Microkinetic Model Accounting for Intraparticle Surface-Intermediates Concentration Profiles

Kechagiopoulos

Thybaut

Marin

2013

Ind. Eng. Chem. Res.

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A microkinetic model for oxidative coupling of methane (OCM) has been developed that comprises a reaction network of 39 gas-phase and 26 catalytic elementary steps. It has been implemented in a heterogeneous reactor model that explicitly accounts for the interactions between gas phase and surface species. Concentration gradients arising from mass transport limitations are found to develop inside the catalyst pellet for all intermediates (i.e., surface and gas-phase) even under an intrinsic kinetics regime for the molecules and clearly affect the C 2 selectivity. Special attention has been devoted to the reduction of the number of adjustable parameters in the model and the a priori determination of thermodynamic as well as kinetic parameters. A contribution analysis is conducted in order to elucidate the complex reaction pathways in OCM that lead to the desired products. Apart from the methyl radicals that couple to an extent of almost 70% in the void space between the pellets, the catalyst pellet accounts for the majority of molecules and radicals conversion, which are produced on the surface and further interact either in the catalyst pores or with other surface species. Almost 95% of CH 4 consumption and more than half of the C 2 H 6 production take place inside the catalyst pellet. A similar analysis is applied to understand the effect of various textural properties of catalysts on the performance of OCM, for example, increasing the catalyst porosity is found beneficial for the C 2 yield, as long as a sufficient CH 4 activation takes place, so that the coupling pathway is promoted over the heterogeneous oxidation of CH 3 •.

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Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Oxidative Coupling of Methane: A Microkinetic Model Accounting for Intraparticle Surface-Intermediates Concentration Profiles

Kechagiopoulos

Thybaut

Marin

2013

Ind. Eng. Chem. Res.

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“…For example, Geerts et al identified the following seven elementary reactions that strongly affect the overall reaction: These were all included in our elementary reaction set. The surface reactions were selected according to previous studies and can be classified into the seven groups as shown in Table . , This model with 166 elementary reactions involves 23 compounds, namely, CH x ( x = 1–4), C 2 H x ( x = 1–6), CHO, CH 2 O, CH 3 O, CO, CO 2 , C, H, H 2 , H 2 O, H 2 O 2 , HO 2 , O, O 2 , and OH. The surface adsorption/desorption of all these gas-phase species were included in the calculation.…”

Section: Methodsmentioning

confidence: 99%

“…The surface reactions were selected according to previous studies and can be classified into the seven groups as shown in Table 1. 21,46 The rate of progress of the ith elementary reaction involving K chemical species can be written in the following general form where k for and k rev are the rate constants for the forward and reverse directions, respectively. C k is the mole concentration of the kth species.…”

Section: T H I S C O N T E N T Imentioning

confidence: 99%

A First-Principles Microkinetics for Homogeneous–Heterogeneous Reactions: Application to Oxidative Coupling of Methane Catalyzed by Magnesium Oxide

Ishikawa

Tateyama

2021

ACS Catal.

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The oxidative coupling of methane (OCM), a major catalytic reaction in natural gas utilization, was examined by first-principles density functional theory (DFT) calculations combined with microkinetic and reactor simulations. We investigated magnesium oxide (MgO), which is a standard catalyst for the OCM reaction. We used the stepped MgO as the catalyst model, as this surface is a strong candidate for the active site for the CH3 generation from CH4. Previous experimental and kinetic simulations have shown that CH3 generated by the surface reactions couples into C2H6 in the gas phase, and thus the OCM is the homogeneous–heterogeneous process. Based on this, we conducted a theoretical study using DFT-based microkinetics by including both gas-phase and surface reactions. The calculations provide theoretical CH4 conversion and C2 selectivity without using any kinetic experimental parameters, which are in reasonable agreement with the experiments. The dependence of these quantities on the reaction condition such as the temperature or inlet gas component is also analyzed, and it has been shown that the CH4 conversion increases at higher temperature; on the other hand, the C2 selectivity decreases. The opposite trend was observed with respect to the partial pressure ratio of CH4 and O2, as the C2 selectivity increases when the partial pressure of CH4 is high. These tendencies are in agreement with the experiments. Consequently, our calculation supports the experimental suggestion that the stepped MgO is the active site for the OCM. We also carried out the analysis on the reaction network, indicating that a large portion of deep oxidation occurs via dehydrogenation of C2 compounds.

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Redox properties and catalytic performance of complex oxides in oxidative coupling of methane

Cited by 2 publications

References 11 publications

Oxidative Coupling of Methane: A Microkinetic Model Accounting for Intraparticle Surface-Intermediates Concentration Profiles

Oxidative Coupling of Methane: A Microkinetic Model Accounting for Intraparticle Surface-Intermediates Concentration Profiles

A First-Principles Microkinetics for Homogeneous–Heterogeneous Reactions: Application to Oxidative Coupling of Methane Catalyzed by Magnesium Oxide

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