Reaction Mechanism for Methane-to-Methanol in Cu-SSZ-13: First-Principles Study of the Z2[Cu2O] and Z2[Cu2OH] Motifs

Engedahl, Unni; Arvidsson, Adam; Grönbeck, Henrik; Hellman, Anders

doi:10.3390/catal11010017

Cited by 2 publications

(6 citation statements)

References 52 publications

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“…Zeolites are known to be very humid, and the presence of water has proven to be important for reactions in the zeolite. 20,27 The dry mechanism as illustrated in Figure 1 The energy landscape for activation of Z 2 [2Cu], with water included in the reaction, is shown in Figure 2. As opposed to the 2Cu system without H 2 O, inclusion of water initially lifts one of the Cu ions from its position in the 6 MRs.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Zeolites are known to be very humid, and the presence of water has proven to be important for reactions in the zeolite. , The dry mechanism as illustrated in Figure might, thus, be affected by the addition of H 2 O. Here, one H 2 O is introduced into the reaction mechanism and is allowed to interact with the reaction intermediates.…”

Section: Resultsmentioning

confidence: 99%

“…The identified DMTM reaction occurs over the CuOOCu and CuOCu structures, and the activity is investigated using a microkinetic model calculating the turnover frequency (TOF) for a continuous reaction cycle. As the presence of water is believed to influence the reaction, ,,, the partial pressure of water is included in a microkinetic model of the activity for the reaction.…”

Section: Introductionmentioning

confidence: 99%

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Complete Reaction Cycle for Methane-to-Methanol Conversion over Cu-SSZ-13: First-Principles Calculations and Microkinetic Modeling

et al. 2021

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The steadily increasing consumption of natural gas imposes a need to facilitate the handling and distribution of the fuel, which presently is compressed or condensed. Alternatively, reduced volatility and increased tractability are achieved by converting the chemical energy of the main component, methane, into liquid methanol. Previous studies have explored direct methane-to-methanol conversion, but suitable catalysts have not yet been identified. Here, the complete reaction cycle for methane-to-methanol conversion over the Cu-SSZ-13 system is studied using density functional theory. The first step in the reaction cycle is the migration of Cu species along the zeolite framework forming the Cu pair, which is necessary for the adsorption of O2. Methane conversion occurs over the CuOOCu and CuOCu sites, consecutively, after which the system is returned to its initial structure with two separate Cu ions. A density functional theory-based kinetic model shows high activity when water is included in the reaction mechanism, for example, even at very low partial pressures of water, the kinetic model results in a turnover frequency of ∼1 at 450 K. The apparent activation energy from the kinetic model (∼1.1 eV) is close to recent measurements. However, experimental studies always observe very small amounts of methanol compared to formation of more energetically preferred products, for example, CO2. This low selectivity to methanol is not described by the current reaction mechanism as it does not consider formation of other species; however, the results suggest that selectivity, rather than inherent kinetic limitations, is an important target for improving methanol yields from humid systems. Moreover, a closed reaction cycle for the partial oxidation of methane has long been sought, and in achieving this over the Cu-SSZ-13, this study contributes one more step toward identifying a suitable catalyst for direct methane-to-methanol conversion.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Complete Reaction Cycle for Methane-to-Methanol Conversion over Cu-SSZ-13: First-Principles Calculations and Microkinetic Modeling

et al. 2021

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“…Copper trimers have, for example, been observed in large-pore structures, such as MFI and MOR whereas monomers and dimers predominantly have been observed in small-pore zeolites, such as chabazite (CHA). In addition to the pore size, the number of Cu atoms in the preferred site is believed to be affected by the Si/Al ratio and the distance between the Al ions in the zeolite framework. , The zeolite is at standard conditions humid, and the presence of water has been reported to affect the oxidation properties of the metal site , as well as the mechanism for methane-to-methanol conversion. , Using density functional theory (DFT) calculations in combination with kinetic modeling, we have shown that the presence of water significantly increases the activity of the Cu dimer site in the CHA framework, by increasing the mobility of the Cu cations, lowering reaction barriers, and facilitating the desorption of methanol …”

Section: Introductionmentioning

confidence: 96%

“…16,17 The zeolite is at standard conditions humid, and the presence of water has been reported to affect the oxidation properties of the metal site 18,19 as well as the mechanism for methane-to-methanol conversion. 20,21 Using density functional theory (DFT) calculations in combination with kinetic modeling, we have shown that the presence of water significantly increases the activity of the Cu dimer site in the CHA framework, by increasing the mobility of the Cu cations, lowering reaction barriers, and facilitating the desorption of methanol. 22 A crucial property of the catalytic site is its ability to change the oxidation state, which is required to adsorb O 2 .…”

Section: ■ Introductionmentioning

confidence: 99%

Investigating the Composition of the Metal Dimer Site in Chabazite for Direct Methane-to-Methanol Conversion

Engedahl,

Boje,

Ström

et al. 2024

J. Phys. Chem. C

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Methanol is a liquid energy carrier that has the potential to reduce the use of fossil fuels. Industrial production of methanol is currently a multistep high-temperature/high-pressure synthesis route. Direct conversion of methane to methanol under low-temperature and low-pressure conditions is an interesting but challenging alternative, which presently lacks suitable catalysts.Here, the complete reaction cycle for direct methane-to-methanol conversion over transition-metal dimers in the chabazite zeolite is studied by using density functional theory calculations and microkinetic modeling. In particular, a reaction mechanism previously identified for the Cu 2 dimer is explored under dry and wet conditions for dimers composed of Ag, Au, Pd, Ni, Co, Fe, and Zn and the bimetallic dimers AuCu, PdCu, and AuPd. The densityfunctional-theory-based microkinetic modeling shows that Cu 2 , AuPd, and PdCu dimers have reasonable turnover frequencies under technologically relevant conditions. The adsorption energy of atomic oxygen is identified as a descriptor for the reaction landscape as it correlates with the adsorption and transition-state energies of the other reaction intermediates. Using the established scaling relations, a volcano plot of the rate is generated with its apex close to the Cu 2 , AuPd, and PdCu dimers.

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Reaction Mechanism for Methane-to-Methanol in Cu-SSZ-13: First-Principles Study of the Z2[Cu2O] and Z2[Cu2OH] Motifs

Cited by 2 publications

References 52 publications

Complete Reaction Cycle for Methane-to-Methanol Conversion over Cu-SSZ-13: First-Principles Calculations and Microkinetic Modeling

Complete Reaction Cycle for Methane-to-Methanol Conversion over Cu-SSZ-13: First-Principles Calculations and Microkinetic Modeling

Investigating the Composition of the Metal Dimer Site in Chabazite for Direct Methane-to-Methanol Conversion

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