Isothermal Cyclic Conversion of Methane into Methanol over Copper‐Exchanged Zeolite at Low Temperature

Tomkins, Patrick; Mansouri, Ali; Bozbağ, Selmi Erim; Krumeich, Frank; Park, Min Bum; Alayon, Evalyn Mae C.; Ranocchiari, Marco; Bokhoven, Jeroen A. van

doi:10.1002/anie.201511065

Cited by 199 publications

(252 citation statements)

References 30 publications

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“…More importantly, the presence of zinc prevented the copper from sintering during the catalytic reaction and ensured its high dispersion as seen from the transmission electron microscopy (TEM) of the fresh calcined and spent catalysts ( Figure 3). Similar copper/copper oxide nanoparticles were reported for ion-exchanged mordenites, 8,27,29 and their presence was suggested to be concomitant with the activity loss in DME carbonylation because of the active species migration from ion-exchanged positions to the external surface and agglomeration. 29 No detectable nanoparticles were observed with the most efficient 1Cu-4Zn/H-MOR catalyst after completion of the catalytic reaction in the reductive CO atmosphere, suggesting their negligible catalytic function.…”

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confidence: 75%

Zinc Hinders Deactivation of Copper-Mordenite: Dimethyl Ether Carbonylation

Reule

Semagina

2016

ACS Catal.

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A plethora of previously unimaginable low-temperature C 1 and C 2 valorization reactions have become possible after the discovery of metal-exchanged solid-acid catalysts, with the most promising candidate being copper-mordenite. We show the dramatic effect of zinc addition to copper-exchanged mordenite in maintaining high Cu dispersion and reducing the catalyst poisoning as it relates to carbonylation of dimethyl ether to methyl acetate. Zinc maintains 90%+ selectivity even during deactivation versus 60% for the Cu-mordenite, which leads to 6-fold higher product yield. The concept of Zn addition is recommended for further exploration in the conversion of methane to methanol or acetic acid.

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confidence: 75%

Zinc Hinders Deactivation of Copper-Mordenite: Dimethyl Ether Carbonylation

Reule

Semagina

2016

ACS Catal.

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“…3 (6,7). In those cases, there is competition between water adsorption driven by exothermicity and desorption driven by the absence of water.…”

Section: à4mentioning

confidence: 99%

Response to Comment on “Selective anaerobic oxidation of methane enables direct synthesis of methanol”

Sushkevich

Palagin

Ranocchiari

et al. 2017

Science

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Periana argues that the stepwise reaction of methane with water is thermodynamically unfavorable and therefore impractical. We reply by presenting an in-depth thermodynamic analysis of each step in the process and show that the surface concentrations of the reactants and products as well as the stabilizing effect of additional water molecules, as discussed in the original paper, fully support the feasibility of the proposed reaction. In the Technical Comment, Periana (1) presents a thermodynamic analysis of two transformations in the oxidation of methane to methanol with water. Whereas the reaction of copper (II) oxide with methane (the first step in chemical looping) was accepted as being thermodynamically possible (Eq. 1, DG 473K = -12 kJ/mol), the reaction of copper(I) oxide with water (the second step in chemical looping) was concluded to be thermodynamically impossible (Eq. 2, DG 473K = +121 kJ/mol). The conclusions reached by Periana about the thermodynamics of bulk oxides were then projected to the Cu I -□-Cu I sites that interact with water in the mordenite zeolite.The thermodynamics represented in Eqs. 1 and 2 are correct under standard conditions; however, the models of the two reaction steps, the conditions, and the reactive species described by Periana are not representative of the material, nor do they fully represent the reaction steps in the chemical looping system described in our paper. The following assumptions were made by Periana, which led to erroneous conclusions: 1) Bulk crystalline copper oxides were used to model the copper sites in mordenite zeolite.2) Gibbs free energy for the system in equilibrium, with total pressure of 1 bar for each component, was applied.3) Specific adsorption of reacting and formed molecules over the surface of the copper-exchanged mordenite zeolite (CuMOR) material was not considered.4) Enthalpic stabilization of intermediate species by water molecules was not taken into account.5) An activation step, including the dehydration of the material, was omitted. We present the thermodynamic analysis of each of the subreactions, taking into account the adsorption phenomena typical of heterogeneous systems. We estimate the Gibbs free energy under the conditions given in our paper, in contrast to the standard DG.Taking into account the experimental details of chemical looping over the CuMOR material, our simplified reaction scheme consists of two main steps (Eqs. 3 and 4), each of which is required for the reaction to occur. The Cu-O-Cu mono-m-oxo sites are assumed to be active sites responsible for such transformations. Equation 3 corresponds to the interaction of activated CuMOR with methane at 7 bar and 473 K . Equation 4 represents the continuous flowing of water vapor at 473 K followed by desorption of methanol and the formation of hydrogen with the reoxidation of the copper sites. All these observations are based on experimental evidence. The standard Gibbs free energy was calculated by density functional theory, and Fig. 3 in (2) presents all the intermediates wit...

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“…Numerous copper‐exchanged zeolites, including CuMFI, CuMOR, CuFAU, CuMAZ, and CuCHA, were tested and revealed different methanol yields and selectivity per cycle. The research targeting the achievement of the highest methanol productivity allowed to obtain the methanol productivity close to the theoretical limit .…”

Section: Introductionmentioning

confidence: 99%

Pathways of Methane Transformation over Copper‐Exchanged Mordenite as Revealed by In Situ NMR and IR Spectroscopy

2019

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The reaction of methane with copper‐exchanged mordenite with two different Si/Al ratios was studied by means of in situ NMR and infrared spectroscopies. The detection of NMR signals was shown to be possible with high sensitivity and resolution, despite the presence of a considerable number of paramagnetic CuII species. Several types of surface‐bonded compounds were found after reaction, namely molecular methanol, methoxy species, dimethyl ether, mono‐ and bidentate formates, CuI monocarbonyl as well as carbon monoxide and dioxide, which were present in the gas phase. The relative fractions of these species are strongly influenced by the reaction temperature and the structure of the copper sites and is governed by the Si/Al ratio. While methoxy species bonded to Brønsted acid sites, dimethyl ether and bidentate formate species are the main products over copper‐exchange mordenite with a Si/Al ratio of 6; molecular methanol and monodentate formate species were observed mainly over the material with a Si/Al ratio of 46. These observations are important for understanding the methane partial oxidation mechanism and for the rational design of the active materials for this reaction.

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Isothermal Cyclic Conversion of Methane into Methanol over Copper‐Exchanged Zeolite at Low Temperature

Cited by 199 publications

References 30 publications

Zinc Hinders Deactivation of Copper-Mordenite: Dimethyl Ether Carbonylation

Zinc Hinders Deactivation of Copper-Mordenite: Dimethyl Ether Carbonylation

Response to Comment on “Selective anaerobic oxidation of methane enables direct synthesis of methanol”

Pathways of Methane Transformation over Copper‐Exchanged Mordenite as Revealed by In Situ NMR and IR Spectroscopy

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