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Solvent effects in catalytic reactions have received widespread attention as they can promote reaction rates and product selectivities by orders of magnitude. It is well accepted that the stable five‐membered cyclic intermediates formed between the solvent molecules and Ti species are crucial to the alkene epoxidation in a heterogeneous Ti(IV)−H2O2 system. However, the direct spectroscopic evidence of these intermediates is still missing and the corresponding reaction pathway for the alkene epoxidation remains unclear. By combining in situ 13C MAS NMR, two‐dimensional (2D) 1H−13C heteronuclear correlation (HETCOR) NMR spectroscopy and theoretical calculations, the five‐membered ring structures, where the protic solvents (ROH), and aprotic solvent (acetone), coordinate and stabilize the active Ti species, are identified for the first time over Ti‐Beta/H2O2 system. Moreover, the role of these cyclic intermediates in the alkene epoxidation/hydration conversion is clarified. These results provide new insights into the solvent effect in liquid‐phase epoxidation/hydration reactions over Ti(IV)−H2O2 system. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Methane dehydroaromatization (MDA) over Mo‐modified zeolite is a potential catalytic route for converting natural gas into valuable aromatics. However, the active species in this reaction are highly complex, involving diverse Mo species, acidic sites of zeolite, and organic molecules. Herein, we apply 1D 95Mo NMR and 2D 1H‐95Mo heteronuclear correlation solid‐state NMR spectroscopy to directly observe the active ensembles in the confined channels of Mo/ZSM‐5 zeolite during the MDA reaction. We monitor the evolution of the spatial correlations of Mo species with the Brønsted acid sites and organic products (olefins and aromatics) in the zeolite channels. We identified two kinds of MoOxCy species, with the more carbidic one (MoOxCy‐II) exhibiting higher activity for methane activation and benzene formation. The strong spatial interactions between the active Mo species and the organic species in the Mo/ZSM‐5 pores are related to the MDA activity. [ABSTRACT FROM AUTHOR]

Catalytic combustion is promising in removing trace amounts of CH4 to address serious environmental concerns. Supported Pd‐based catalysts are most effective but often suffer from low stability in applications owing to the water‐vapor‐induced sintering. Herein, we develop a universal strategy to prepare irreducible‐oxide‐modified Pd/MgAl2O4 catalysts which show high activity and excellent stability against both hydrothemal aging at elevated temperatures and deactivation in long‐term reaction under wet conditions. The addition of irreducible oxides inhibited the deep oxidation of Pd in the oxygen‐rich conditions, which preserved not only the epitaxial structure but also a suitable active phase of Pd‐PdOx on MgAl2O4, thus promoting both activity and stability. This work provides new insights into the effect of metal–oxide interaction on CH4 combustion and offers an avenue to design hydrothermally stable and active combustion catalysts for industrial applications. [ABSTRACT FROM AUTHOR]

Hydrocarbon-pool chemistry is important in methanol to olefins (MTO) conversion on acidic zeolite catalysts. The hydrocarbon-pool (HP) species, such as methylbenzenes and cyclic carbocations, confined in zeolite channels during the reaction are essential in determining the reaction pathway. Herein, we experimentally demonstrate the formation of supramolecular reaction centers composed of organic hydrocarbon species and the inorganic zeolite framework in H-ZSM-5 zeolite by advanced 13C-27Al double-resonance solid-state NMR spectroscopy. Methylbenzenes and cyclic carbocations located near Brønsted acid/base sites form the supramolecular reaction centers in the zeolite channel. The internuclear spatial interaction/proximity between the 13C nuclei (associated with HP species) and the 27Al nuclei (associated with Brønsted acid/base sites) determines the reactivity of the HP species. The closer the HP species are to the zeolite framework Al, the higher their reactivity in the MTO reaction. [ABSTRACT FROM AUTHOR]