Methoxy Species Research Articles

Methanol steam reforming over copper supported on apatites

Low-temperature methanol steam (MSR) reforming over Cu is an efficient process for releasing H2 from this promising liquid hydrogen carrier but the Cu contents of commercial catalysts are often exceedingly high. Here we show that Sr-exchanged fluoro and hydroxyapatites with 1wt.% Cu exhibit very high methanol turnover frequencies up to 386h-1 and H2 production rates up to 6569mol H2 kgCu-1 h-1 with CO selectivity as low as ~0.25% at 250 °C. Formaldehyde and methyl formate are the only other byproducts which are especially observed over catalysts with low Sr/P ratio in the hydroxyapatite. The reforming proceeds through methoxy, formaldehyde and formate species according to in situ FTIR and mass spectrometric measurements. The spectroscopic analyses further reveal the involvement of apatitic HPO42- ions in the catalytic sequence. Thus, the catalytic synergy between Cu and apatites provides a basis for highly efficient, bifunctional MSR catalysts with low copper content.

Accelerator or inhibitor? The effects of H2O on selective catalytic reduction of NOx by methanol over HZSM-5 catalysts with different Lewis/Brønsted ratios

HZSM-5 zeolites are widely regarded as promising catalysts for the selective catalytic reduction of NOx using methanol (CH3OH-SCR). However, the effect of H2O on CH3OH-SCR over HZSM-5 zeolites with varying Lewis and Brønsted acid sites (LAS and BAS) remains unclear. Herein, a series of HZSM-5 catalysts with varying LAS/BAS ratios were synthesized through Ga modification combined with calcination. Notably, these catalysts with varying LAS/BAS ratios exhibit diverse CH3OH-SCR activity. The HZSM-5 catalyst with a higher amounts BAS shows superior SCR performance (93 % NOx conversion at 300 ℃) under dry conditions, while Ga/HZSM-5 with abundant LAS demonstrate better De-NOx activity in the presence of H2O. In situ DRIFTS results, TPSR-MS coupled with DFT calculations demonstrate that the Si(OH)Al sites in HZSM-5 zeolites promote the generation of intermediate formamide under dry conditions. Whereas, the extra-framework Al-OH and Ga species in Ga/HZSM-5 catalysts lead to excessive oxidation of methanol to formate species. When water is present, intense competitive adsorption between CH3OH and H2O occurs at the Si(OH)Al sites, significantly decreasing the denitration activity of HZSM-5. However, H2O not only alleviates the over-oxidation of methoxy species, but also enables the Al-OH and GaO+ sites to adsorb and activate CH3OH to generate formamide species, thereby exhibiting preferable catalytic activity in Ga/HZSM-5 catalysts. Accordingly, a reaction mechanism based on the synergistic effect of BAS and LAS is proposed for Ga/HZSM-5 catalysts.

Breaking the Conversion-Selectivity Trade-Off in Methanol Synthesis from CO2 Using Dual Intimate Oxide/Metal Interfaces.

The selective hydrogenation of carbon dioxide (CO2) to value-added chemicals, e.g., methanol, using green hydrogen retrieved from renewable resources is a promising approach for CO2 emission reduction and carbon resource utilization. However, this process suffers from the competing side reaction of reverse water-gas shift (RWGS) and methanol decomposition, which often leads to a strong conversion-selectivity trade-off and thus a poor methanol yield. Here, we report that InOx coating of PdCu bimetallic nanoparticles (NPs) to construct intimate InOx/Cu and InOx/PdIn dual interfaces enables the break of conversion-selectivity trade-off by achieving ∼80% methanol selectivity at ∼20% CO2 conversion close to the thermodynamic limit, far superior to that of conventional metal catalysts with a single active metal/oxide interface. Comprehensive microscopic and spectroscopic characterization revealed that the InOx/PdIn interface favors the activation of CO2 to formate, while the adjacent InOx/Cu interface readily converts formate intermediates to methoxy species in tandem, which thus cooperatively boosts methanol production. These findings of dual-interface synergies via oxide coating of bimetallic NPs open a new avenue to the design of active and selective catalysts for advanced catalysis.

Confinement-Driven Dimethyl Ether Carbonylation in Mordenite Zeolite as an Ultramicroscopic Reactor.

ConspectusThe conversion of C1 molecules to methyl acetate through the carbonylation of dimethyl ether in mordenite zeolite is an appealing reaction and a crucial step in the industrial coal-to-ethanol process. Mordenite zeolite has large 12-membered-ring (12MR) channels (7.0 × 6.5 Å2) and small 8MR channels (5.7 × 2.6 Å2) connected by a side pocket (4.8 × 3.4 Å2), and this unique pore architecture supplies its high catalytic activity to the key step of carbonylation. However, the reaction mechanism of carbonylation in mordenite zeolite is not thoroughly established in that it is able to explain all experimental phenomena and improve its industrial applications, and the classical potential energy surface exerted by static density function theory calculations cannot reflect the reaction kinetics under realistic conditions because the diffusion kinetics of bulk DME (kinetic dimeter: 4.5 Å) and methyl acetate (MA, kinetic dimeter: 5.5 Å) were not well considered and their restricted diffusion in the narrow side pocket and 8MR channels may greatly alter the integrated kinetics of DME carbonylation in mordenite zeolite. Moreover, the precise illustration of the dynamic behaviors of the ketene intermediate and its derivatives (surface acetate and acylium ion) confined within various voids in mordenite has not been effectively portrayed.Advanced ab initio molecular dynamics (AIMD) simulations with or without the acceleration of enhanced sampling methods provide tremendous opportunities for operando modeling of both reaction and diffusion processes and further identify the geometrical structure and chemical properties of the reactants, intermediates, and products in the different confined voids of mordenite under realistic reaction conditions, which enables high consistency between computations and experiments.In this Account, the carbonylation process in mordenite is comprehensively described by the results of decades of continuous research and newly acquired knowledge from both multiscale simulations and in-(ex-)situ spectroscopic experiments. Three primary steps (DME demethylation to surface methoxy species (SMS), carbon-carbon bond coupling between SMS and CO to acetyl species, and methyl acetate formation by acetyl species and methanol/DME) have been respectively studied with a careful consideration of different molecular factors (reactant distribution, concentration, and attack mode). By utilizing the free-energy surface of diffusion and reaction obtained from AIMD simulations, a comprehensive reaction/diffusion kinetic model was formulated for the first time, illustrating the entire zeolite catalytic process. In this context, a comprehensive and informative analysis of the reaction kinetics of carbonylation in mordenite, including the function of the 12MR channels, 8MR channels, and side pockets in the adsorption, diffusion, and reaction of DME carbonylation, was performed. The different channels of mordenite play different roles in all ordered reaction steps, illustrating a highly organized ultramicroscopic reactor that is encompassed.

Regulating anisotropic diffusion in zeolite for reinforced para-xylene synthesis via CO2 hydrogenation in the presence of toluene

The synthesis of valuable aromatics via CO2 transformation, especially para-xylene (PX), is of paramount significance but still remains greatly challenging due to the low efficiency and poor selectivity. The present work utilized a composite catalyst based on ZnZrOx with a modified H-ZSM-5 exhibiting nano-prism stacking to realize the selective synthesis of PX. Methoxy species generated from CO2-derived formate produced as an intermediate over the ZnZrOx were readily incorporated into the xylene products for effective alkylation, contributed to an enhanced aromatics-based cycle that provided a selectivity for xylenes among all C5+ hydrocarbons of 91.1 %. The lengthened straight channels in the H-ZSM-5 along the b-axis, derived from the crystal stacking pattern, increased differences in the diffusion properties of the xylene isomers, and thereby steering the movement of molecules toward a product shape-selective pathway, leading to 90.1 % selectivity for PX among all xylenes, and provided exceptional CO2 utilization efficiency of ∼60 %.

Surface Reconstruction-Induced Photocatalytic Methanol Reduction Reaction on a Rutile TiO2(001) Surface.

Photochemistry of methanol on TiO2 surfaces is of great importance both fundamentally and industrially. Methanol was previously reported only to occur photogenerated hole-participating oxidation reactions on TiO2 surfaces. Herein, we report that, upon UV light illumination, the methoxy species formed by methanol dissociation at the 5-fold coordinated Ti4+ sites (CH3O(a)Ti5c) of a reconstructed rutile TiO2(001)-(1 × 1) surface also undergoes the C-O bond cleavage into methyl fragments mediated by photogenerated electrons, in addition to the well-established photogenerated hole-participating oxidation reactions. Upon subsequent heating, the resulting methyl species undergoes hydrogenation and coupling reactions into methane and ethane, respectively. Accompanying theoretical calculations showed that the lowest unoccupied molecular orbital (LUMO) of CH3O(a)Ti5c is localized almost at the conduction band minimum of the CH3O-adsorbed reconstructed rutile TiO2(001)-(1 × 1) surface, indicating the likely TiO2 → CH3O(a)Ti5c interfacial photoexcited-electron transfer. These results greatly broaden the photochemistry of methanol on TiO2 surfaces and demonstrate a photocatalytic methanol-to-hydrocarbon reaction route.

Mechanistic investigation of methanol-to-olefins conversion catalyzed by H-ZSM-5 zeolite: a DFT study.

The mechanisms for the formation of the first C - C bond and lower olefins on methanol to olefins (MTO) conversion on H-ZSM-5 had been focused in dispute. In this paper, density functional theory has been used to study the reaction mechanisms of methanol to olefins on ZSM-5. The configurations of reactants, intermediates, products and transition state of the numerous reactions involved in such a process have been optimized, as well as the elementary reactions related to these configurations were determined by the calculation of corresponding activation energy barriers and reaction heats. Here, two different kinds of the mechanisms were proposed for the formation of dimethylether (DME), one involving an associative interaction of two methanol molecules with the zeolite Brønsted acid sites and the other occurring via a surface methoxy species and a methanol molecule. A critical intermediate of the methoxy methyl cation was theoretically verified by the reaction of the methoxy species and dimethylether. Besides, it was found that the first intermediates containing a C - C bond were 1,2-dimethoxyethane and 2-methoxy-ethanolare, in which the former was formed from methoxy species with dimethyl ether and the latter was formed from methanol by onium ions((CH3)2O+CH2CH2OCH3), respectively. For the whole reaction mechanism, the results in this paper indicated that the ethene formation is more favorable than propylene formation due to the low activation energy barrier for ethene formation (123.49 vs. 162.09kJ.mol-1). From these calculations, it would be concluded that ethene is the first alkene product that induces the occurrence of the hydrocarbon pool mechanism. All the periodic density function theory (DFT) calculations were performed by the Vienna Ab Initio Simulation package (VASP). The interaction between nucleus and valence electron was described using the pseudopotentials found in the projector augmented wave (PAW) method. PBE-D3 was used in the whole DFT calculations and CI-NEB was used to locate transition state.

Confinement driving mechanism of surface methoxy species formation in mordenite zeolite: An interplay of different molecular factors

Surface methoxy species (SMS) are key intermediates in methanol conversion within zeolites. We propose a reaction mechanism for SMS formation using methanol or dimethyl ether in mordenite zeolites, based on ab initio molecular dynamics (AIMD) simulations and validated by in situ experiments. Key factors such as adsorption, diffusion, distribution, and attacking modes of reactants were considered. The forward attacking mode of both methanol and dimethyl ether on the acid site is more feasible for SMS formation than the backward mode in the 8 member-ring of mordenite (MOR-8MR). For methanol, two end-to-end molecules in MOR-8MR promote SMS formation via a stepwise pathway, avoiding the rotation of protonated methanol, while two methanol molecules on different sides of acid site hinder SMS formation. Dimethyl ether, however, converts to SMS in MOR-8MR regardless of concentration and distribution. The kinetics align with in situ Fourier transform infrared experiments and are confirmed by two-dimensional correlation analysis of methanol dehydration.

The Pd/ZrO2 catalyst inversely loaded with various metal oxides for methanol synthesis from carbon dioxide

The selectivity and stability of catalysts for methanol synthesis from CO2 still remain to be enhanced. In this work, we synthesized a series of Pd/ZrO2 catalysts inversely loaded with various metal oxide promoters (ZnO, In2O3, and CeO2), those would partially cover Pd metal surface and form some new metal-promoter interface, to explore the nature in the performance of CO2 hydrogenation to methanol. The catalyst synthesized by this approach could limit the growth of Pd particles during the reduction and form new metal–metal oxide interfaces with different functions of CO2 hydrogenation, improving the reaction performance of Pd-ZrO2 catalysts. As a result, the ZnO-Pd/ZrO2 catalyst exhibited the highest CO2 conversion (12.0 %), methanol selectivity (95.6 %), and STY of methanol (472 gMeOHkgcat-1h−1), with excellent stability. The results of HRTEM, H2-TPR, XPS, and XAFS showed that the ZnO-Pd/ZrO2 catalyst had the typical Pd-ZnO interface with Pd2+ species after the H2 reduction, which could enhance the adsorption and activation of CO2. In addition, the in situ DRIFTS and NAP-XPS results implied that the Pd-ZnO interface significantly improved the formation of formate (HCOO*) and methoxy (H3CO*) species, which were considered to be the key intermediates of methanol generation, and thus greatly enhanced the selectivity of methanol.

Dimethyl Carbonate Synthesis from CO2 over CeO2 with Electron-Enriched Lattice Oxygen Species.

Direct synthesis of dimethyl carbonate (DMC) from CO2 plays an important role in carbon neutrality, but its efficiency is still far from the practical application, due to the limited understanding of the reaction mechanism and rational design of efficient catalyst. Herein, abundant electron-enriched lattice oxygen species were introduced into CeO2 catalyst by constructing the point defects and crystal-terminated phases in the crystal reconstruction process. Benefitting from the acid-base properties modulated by the electron-enriched lattice oxygen, the optimized CeO2 catalyst exhibited a much higher DMC yield of 22.2 mmol g-1 than the reported metal-oxide-based catalysts at the similar conditions. Mechanistic investigations illustrated that the electron-enriched lattice oxygen can provide abundant sites for CO2 adsorption and activation, and was advantageous of the formation of the weakly adsorbed active methoxy species. These were facilitating to the coupling of methoxy and CO2 for the key *CH3OCOO intermediate formation. More importantly, the weakened adsorption of *CH3OCOO on the electron-enriched lattice oxygen can switch the rate-determining-step (RDS) of DMC synthesis from *CH3OCOO formation to *CH3OCOO dissociation, and lower the corresponding activation barriers, thus giving rise to a high performance. This work provides insights into the underlying reaction mechanism for DMC synthesis from CO2 and methanol and the design of highly efficient catalysts.

Dimethyl Carbonate Synthesis from CO2 over CeO2 with Electron‐Enriched Lattice Oxygen Species

AbstractDirect synthesis of dimethyl carbonate (DMC) from CO2 plays an important role in carbon neutrality, but its efficiency is still far from the practical application, due to the limited understanding of the reaction mechanism and rational design of efficient catalyst. Herein, abundant electron‐enriched lattice oxygen species were introduced into CeO2 catalyst by constructing the point defects and crystal‐terminated phases in the crystal reconstruction process. Benefitting from the acid‐base properties modulated by the electron‐enriched lattice oxygen, the optimized CeO2 catalyst exhibited a much higher DMC yield of 22.2 mmol g‐1 than the reported metal‐oxide‐based catalysts at the similar conditions. Mechanistic investigations illustrated that the electron‐enriched lattice oxygen can provide abundant sites for CO2 adsorption and activation, and was advantageous of the formation of the weakly adsorbed active methoxy species. These were facilitating to the coupling of methoxy and CO2 for the key *CH3OCOO intermediate formation. More importantly, the weakened adsorption of *CH3OCOO on the electron‐enriched lattice oxygen can switch the rate‐determining‐step (RDS) of DMC synthesis from *CH3OCOO formation to *CH3OCOO dissociation, and lower the corresponding activation barriers, thus giving rise to a high performance. This work provides insights into the underlying reaction mechanism for DMC synthesis from CO2 and methanol and the design of highly efficient catalysts.

Full valorisation of waste PET into dimethyl terephthalate and cyclic arylboronic esters

Developing efficient and cost-effective methodologies for high value-added conversion of waste plastic delivers substantial environmental and economic benefits. Herein, we develop a novel approach utilizing boric acid in the methanolysis of waste polyethylene terephthalate (PET) to derive pure dimethyl terephthalate (DMT) and boronic acid esters through in-situ capture of ethylene glycol (EG). It not only upcycles waste PET but also eliminates intricate EG purification processes. Catalyzed by magnalium-aluminum-layered double oxides (Mg4Al1-LDO), this method achieved 100 % conversions of PET with 96 % and 99 % yields of arylboronic esters and DMT, respectively. Kinetic studies and in-situ Fourier-transform infrared spectroscopy (FT-IR) demonstrated the pivotal role of the monodentate methoxy species, generated through the interaction of medium basic Mg–O ion pairs and methanol. This method demonstrates applicability for the upcycling of assorted discarded PET wastes, polyesters, and polycarbonates with EG units, highlighting its potential as a comprehensive solution for waste plastic management.

Exploring dolomite as a promising support for Ni catalysts in CO2 methanation

Ni catalysts supported on Al-modified calcined dolomite were developed, using a natural mineral as the precursor. Treatment with 3% w/w Al improved thermal stability and increased the surface area. The variation in Ni loading (5–30% w/w) was studied to characterize the structural, morphological, and chemical properties. The CO2 capture capacity of the solids, evaluated by Thermogravimetric Analysis at 400 °C (100–800 μmol∙g−1), decreased with increasing Ni loading due to the reduction of basic sites. CO2-TPD analyses revealed the presence of captured CO2 in various basic sites, especially in the strong ones, with efficient formation of thermally stable carbonates. In catalytic tests at 400 °C, conversions exceeding 50% were achieved for higher Ni loadings and around 50% for lower loadings, with 100% selectivity towards CH4. The application of in situ and operando Diffuse reflectance infrared Fourier transform spectroscopy techniques provided insights into the formation of carbonates and their transformation into formate, methoxy, and formyl species, explaining the total selectivity towards CH4 and the absence of CO in the products. This comprehensive approach significantly contributes to the understanding of the reaction dynamics and opens new perspectives for the utilization of Ni catalysts supported on modified dolomite.

Mechanistic understanding of the thermal-assisted photocatalytic oxidation of methanol-to-formaldehyde with water vapor over Pt/SrTiO3.

Anaerobic thermal-assisted photocatalytic methanol conversion in the gas phase in the presence of water vapor has been suggested as an interesting way to generate formaldehyde as a valuable coupled product in addition to H2 production. Here, the reaction mechanism and photocatalyst deactivation are investigated in detail using in situ diffuse reflectance infrared fourier transform (DRIFTS) and electron paramagnetic resonance (EPR) spectroscopy. EPR shows that paramagnetic oxygen vacancies are not involved in the reaction mechanism over undoped SrTiO3. Instead, on an optimized 0.1 wt% Pt/SrTiO3 photocatalyst, methoxy species are formed by dissociative adsorption of methanol leading to formaldehyde formation while the formation of CO, CO2 (via a formate intermediate) and methyl formate occurs through three concurrent reactions from formyl species. Our findings suggest that CO adsorbed on Pt is a spectator species not perturbing the reaction kinetics, and deactivation is shown to be strongly correlated with the accumulation of formate groups on SrTiO3, which is more pronounced at high reaction temperatures. The mechanistic understanding provided here forms the basis for the further optimization of photocatalysts to increase methanol conversion and improve formaldehyde selectivity.

Difference in reaction mechanism between ZnZrOx and InZrOx for CO2 hydrogenation.

Oxide solid-solution catalysts, such as Zn-doped ZrO2 (ZnZrOx) and In-doped ZrO2 (InZrOx), exhibit distinctive catalytic capabilities for CH3OH synthesis via CO2 hydrogenation. We investigated the active site structures of these catalysts and their associated reaction mechanisms using both experimental and computational approaches. Electron microscopy and X-ray absorption spectroscopy reveal that the primary active sites are isolated cations, such as Zn2+ and In3+, dissolved in tetragonal ZrO2. Notably, for Zn2+, decomposition of the methoxy group, which is an essential intermediate in CH4 synthesis, is partially suppressed because of the relatively high stability of the methoxy group. Conversely, the methyl group strongly adsorbs on In3+, facilitating the conversion of the methoxy species into methyl groups. The decomposition of CH3OH is also suggested to contribute to CH4 synthesis. These results highlight the generation of CH4 as a byproduct of the InZrOx catalyst. Understanding the active site structure and elucidating the reaction mechanism at the atomic level are anticipated to contribute significantly to the future development of oxide solid-solution catalysts.

Infrared Fingerprints of the CO2 Conversion into Methanol at Cu(s)/ZrO2(s): An Experimental and Theoretical Study

AbstractThe methanol economy is an attractive approach to tackle the current concerns over the depletion of natural resources and the global warming intrinsically associated with the use of fossil fuels. This can be achieved by hydrogenation of carbon dioxide to produce methanol, a liquid fuel with potential use in civil transportation. In this study, we aim to pinpoint the intermediates that are involved in the catalytic CO2 conversion into methanol on pure zirconia (ZrO2), Cu and Cu/ZrO2 systems. To accomplish this, we make use of infrared (IR) spectroscopy measurements and quantum chemical simulations within the hybrid density functional theory (DFT) framework. At 250 °C and p~30 bar, the main species formed on the partially hydroxylated ZrO2 is bidentate formate, whereas the co‐production of bicarbonate is relevant upon cooling to T=25 °C. On pure Cu, the IR fingerprints of methanol and carbon dioxide indicate their presence in the gas phase and surface environment, albeit formate/formic acid and methoxy species are also detected at these experimental conditions. The production of methanol on Cu/ZrO2 is mostly dependent on the Cu catalyst, but the higher amount of the methoxy intermediate can be correlated with the consumption of formate adsorbed on ZrO2 or at the Cu/ZrO2 interface. On the Cu/ZrO2 mixture, the reaction mechanism is likely to involve formate as the main intermediate, instead of CO which would result from the reverse water‐gas shift reaction. Ultimately, the higher activity shown by the Cu/ZrO2 mixture might be associated with the extra‐production of methoxy/methanol catalyzed by ZrO2 in the presence of Cu.

Water‐Induced Micro‐Hydrophobic Effect Regulates Benzene Methylation in Zeolite

AbstractWater is a ubiquitous component in heterogeneous catalysis over zeolites and can significantly influence the catalyst performance. However, the detailed mechanism insights into zeolite‐catalyzed reactions under microscale aqueous environment remain elusive. Here, using multiple dimensional solid‐state NMR experiments coupled with ultrahigh magic angle spinning technique and theoretical simulations, we establish a fundamental understanding of the role of water in benzene methylation over ZSM‐5 zeolite under water vapor conditions. We show that water competes with benzene for the active sites of zeolite and facilitates the bimolecular reaction mechanism. The growth of water clusters induces a micro‐hydrophobic effect in zeolite pores, which reorients benzene molecules and drives their interactions with surface methoxy species (SMS) on zeolite. We identify the formation and evolution of active SMS‐Benzene complexes in a microscale aqueous environment and demonstrate that their accumulation in zeolite pores boosts benzene conversion and methylation.

Water-Induced Micro-Hydrophobic Effect Regulates Benzene Methylation in Zeolite.

Water is a ubiquitous component in heterogeneous catalysis over zeolites and can significantly influence the catalyst performance. However, the detailed mechanism insights into zeolite-catalyzed reactions under microscale aqueous environment remain elusive. Here, using multiple dimensional solid-state NMR experiments coupled with ultrahigh magic angle spinning technique and theoretical simulations, we establish a fundamental understanding of the role of water in benzene methylation over ZSM-5 zeolite under water vapor conditions. We show that water competes with benzene for the active sites of zeolite and facilitates the bimolecular reaction mechanism. The growth of water clusters induces a micro-hydrophobic effect in zeolite pores, which reorients benzene molecules and drives their interactions with surface methoxy species (SMS) on zeolite. We identify the formation and evolution of active SMS-Benzene complexes in a microscale aqueous environment and demonstrate that their accumulation in zeolite pores boosts benzene conversion and methylation.

Epoxidation of Light Olefin Mixtures with Hydrogen Peroxide on TS-1 Catalyst

The direct epoxidation of mixed ethene and propene feedstocks using hydrogen peroxide over a titanium silicalite (TS-1) catalyst was investigated within a continuous trickle bed reactor operating in laboratory scale. Methanol was employed as the reaction solvent. This study aimed to streamline the epoxidation process by obviating the need for prior separation of alkenes, thereby enhancing process efficiency. An extensive array of operational parameters was explored in a trickle bed reactor, encompassing experimental parameters such as temperature, total pressure, hydrogen peroxide concentration, liquid flow rate, and gas composition. In contrast to prior investigations involving separate ethene and propene epoxidation, this study revealed a reduction in epoxide selectivity. The principal by-products observed were methoxy species, formed through the interaction between the epoxide and methanol, resulting in a ring-opening reaction. The influence of water on this ring-opening process was negligible. Notably, the tunability of the system was demonstrated, highlighting low temperature and elevated partial ethene pressure as pivotal factors for augmentingthe epoxide selectivity. The findings suggest that binary olefin mixtures exhibit diminished selectivity but improved stability. This behavior is potentially linked to the olefin solubility in methanol, or alterations in the surface species concentrations, typically associated with catalyst activity variations. These insights offer a valuable foundation for understanding and optimizing the direct epoxidation of mixed ethene and propene feedstock.Graphical

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

AbstractCopper(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.