Oxygen Isotope Exchange over Copper-Containing Mordenite: The Effect of Copper Loading and Si/Al Ratio

Artsiusheuski, Mikalai A.; Bokhoven, Jeroen A. van; Sushkevich, Vitaly L.

doi:10.1021/acs.jpcc.1c08529

Cited by 5 publications

(3 citation statements)

References 71 publications

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“…47,48 The difference in the copper speciation may induce changes in oxygen mobility, which was studied using temperatureprogrammed isotope exchange (TPIE). 49,50 Figure 2A,B represents the fraction of the single-labeled oxygen isotopologue versus temperature during TPIE experiments over the series of copper-containing MFI zeolites with different copper loadings and Si/Al ratios. The proton form of the MFI zeolite is almost inactive in oxygen isotope exchange, and any measurable rate of exchange is observed only at temperatures above 1000 K, while the presence of copper sites induces the mobility of oxygen atoms.…”

Section: Resultsmentioning

confidence: 99%

Structure of Selective and Nonselective Dicopper (II) Sites in CuMFI for Methane Oxidation to Methanol

2022

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The one-step valorization of natural gas remains a challenge. Methane conversion to methanol via chemical looping over copper-containing zeolites is a promising route, and CuMFI is among the earliest successfully applied. However, the structure of the active sites in CuMFI, as well as the effect of copper loading and Si/Al ratio on the copper speciation, are yet to be understood. We found that for CuMFI, the Cu/Al ratio determines the selectivity of methane conversion by governing the structure of the active dicopper sites. At a Cu/Al ratio below 0.3, copper-containing MFI materials host dimeric centers with a Cu–Cu separation of 2.9 Å and a UV/vis absorption band at 27 200 cm–1 capable of selective oxidation of methane to methanol in a wide temperature range (450–550 K). A higher Cu/Al ratio leads to the formation of mono-μ-oxo dicopper sites with Cu–Cu = 3.2 Å, which exhibit a characteristic band at 21 900 cm–1 and react with methane at lower temperatures (<450 K), yielding overoxidation products. Identifying distinctions in the structure of selective and nonselective copper sites will aid in the design of better-performing materials.

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Section: Resultsmentioning

confidence: 99%

Structure of Selective and Nonselective Dicopper (II) Sites in CuMFI for Methane Oxidation to Methanol

2022

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“…In the CoO x /CeO 2 sample, on the contrary, 16 O 18 O appear first, and f 34 is higher than f 32 for all period of monitoring. Klier and Muzykantov [21,28] proposed the theory of isotope exchange of oxygen with solid oxides, which is currently widely used for the interpretation of mechanisms of oxygen transfer in solids [29][30][31]. With this theory, there are three kinetically distinct types of exchange depending on the number of oxygen atoms from the solid phase participating in the exchange reaction, zero-atom (R 0 ), single-atom (R I ), and two-atom (R II ).…”

Section: Qualitative Analysis Of Oxygen Isotope Exchange Processmentioning

confidence: 99%

Kinetics of Oxygen Exchange and N2O Decomposition Reaction over MeOx/CeO2 (Me = Fe, Co, Ni) Catalysts

et al. 2023

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MeOx/CeO2 (Me = Fe, Co, Ni) samples were tested in an 18O2 temperature-programmed isotope exchange and N2O decomposition (deN2O). A decrease in the rate of deN2O in the presence of oxygen evidences the competitive adsorption of N2O and O2 on the same sites. A study of isotope oxygen exchange revealed dissociative oxygen adsorption with the subsequent formation of surface oxygen species. The same species, more probably, result from N2O adsorption and the following N2 evolution to the gas phase. We supposed the same mechanism of O2 formation from surface oxygen species in both reactions, including the stages responsible for its mobility. A detailed analysis of the kinetics of isotope exchange has been performed, and the rates of one-atom (RI) and two-atom (RII) types of exchange were evaluated. The rate of the stage characterizing the mobility of surface oxygen was calculated, supposing the same two-step mechanism was relevant for both types of exchange. The effect of oxygen mobility on the kinetics of deN2O was estimated. An analysis of the possible pathways of isotope transfer from MeOx to CeOx showed that direct oxygen exchange on the Me–Ce interface makes a valuable contribution to the rate of this reaction. The principal role of the Me–Ce interface in deN2O was confirmed with independent experiments on FeOx/CeO2 samples with a different iron content.

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“…[15][16][17] The first step is activation of copper-containing zeolite in oxidative environment at temperature 673 K or higher, resulting in the formation of copper(II)-oxo species. [18,19] In the case of the widely utilized coppercontaining MOR [20][21][22] zeolite most favorable centers are mono-μ-oxo dicopper(II) sites. The second stage is the reaction between activated material and methane.…”

Section: Introductionmentioning

confidence: 99%

Selective Oxidative Dehydrogenation of Ethane and Propane over Copper‐Containing Mordenite: Insights into Reaction Mechanism and Product Protection

Artsiusheuski,

Verel,

van Bokhoven

et al. 2023

Angew Chem Int Ed

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Copper(II)‐containing mordenite (CuMOR) is capable of activation of C−H bonds in C1‐C3 alkanes, albeit there are remarkable differences between the functionalization of ethane and propane compared to methane. The reaction of ethane and propane with CuMOR results in the formation of ethylene and propylene, while the reaction of methane predominantly yields methanol and dimethyl ether. By combining in situ FTIR and MAS NMR spectroscopies as well as time‐resolved Cu K‐edge X‐ray absorption spectroscopy, the reaction mechanism was derived, which differs significantly for each alkane. The formation of ethylene and propylene proceeds via oxidative dehydrogenation of the corresponding alkanes with selectivity above 95 % for ethane and above 85 % for propane. The formation of stable π‐complexes of olefins with CuI sites, formed upon reduction of CuII‐oxo species, protects olefins from further oxidation and/or oligomerization. This is different from methane, the activation of which proceeds via oxidative hydroxylation leading to the formation of surface methoxy species bonded to the zeolite framework. Our findings constitute one of the major steps in the direct conversion of alkanes to important commodities and open a novel research direction aiming at the selective synthesis of olefins.

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Oxygen Isotope Exchange over Copper-Containing Mordenite: The Effect of Copper Loading and Si/Al Ratio

Cited by 5 publications

References 71 publications

Structure of Selective and Nonselective Dicopper (II) Sites in CuMFI for Methane Oxidation to Methanol

Structure of Selective and Nonselective Dicopper (II) Sites in CuMFI for Methane Oxidation to Methanol

Kinetics of Oxygen Exchange and N2O Decomposition Reaction over MeOx/CeO2 (Me = Fe, Co, Ni) Catalysts

Selective Oxidative Dehydrogenation of Ethane and Propane over Copper‐Containing Mordenite: Insights into Reaction Mechanism and Product Protection

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