Insight into the Formation of Nanostructured MFI Sheets and MEL Needles Driven by Molecular Recognition.

Mesoporous and nanostructured zeolite-based catalysts experience prolonged lifetimes due to increased mass transfer and reduced micropore obstruction by coke formation as compared to their bulky microporous counterparts. Diquaternary ammonium structure-directing agents (SDAs) can be used to synthesize hierarchical MFI sheet-like and MEL needle-like zeolites. An explanation of the underlying molecular-level details of the synthesis of these nanostructured zeolites is presented on the basis of non-covalent interactions between the template and zeolite surfaces as well as silicate oligomers studied by means of classical molecular dynamics.

Correlations between Density-Based Bond Orders and Orbital-Based Bond Energies for Chemical Bonding Analysis.

Quantum chemistry-based codes and methods provide valuable computational tools to estimate reaction energetics and elucidate reaction mechanisms. Electronic structure methods allow directly studying the chemical transformations in molecular systems involving breaking and making of chemical bonds and the associated changes in the electronic structure. The link between the electronic structure and chemical bonding can be provided through the crystal orbital Hamilton population (COHP) analysis that allows quantifying the bond strength by computing Hamilton-weighted populations of localized atomic orbitals.

Mechanistic Insight into the [4 + 2] Diels-Alder Cycloaddition over First Row d-Block Cation-Exchanged Faujasites.

The Diels-Alder cycloaddition (DAC) is a powerful tool to construct C-C bonds. The DAC reaction can be accelerated in several ways, one of which is reactant confinement as observed in supramolecular complexes and Diels-Alderases. Another method is altering the frontier molecular orbitals (FMOs) of the reactants by using homogeneous transition-metal complexes whose active sites exhibit d-orbitals suitable for net-bonding orbital interactions with the substrates.

Structure and Evolution of Confined Carbon Species during Methane Dehydroaromatization over Mo/ZSM-5.

Surface carbon (coke, carbonaceous deposits) is an integral aspect of methane dehydroaromatization catalyzed by Mo/zeolites. We investigated the evolution of surface carbon species from the beginning of the induction period until the complete catalyst deactivation by the pulse reaction technique, TGA, C NMR, TEM, and XPS. Isotope labeling was performed to confirm the catalytic role of confined carbon species during MDA.

Electronic Structure Analysis of the Diels-Alder Cycloaddition Catalyzed by Alkali-Exchanged Faujasites.

The Diels-Alder cycloaddition (DAC) reaction is a commonly employed reaction for the formation of C-C bonds. DAC catalysis can be achieved by using Lewis acids and via reactant confinement in aqueous nanocages. Low-silica alkali-exchanged faujasite catalysts combine these two factors in one material.

Stability of CoP Electrocatalysts in Continuous and Interrupted Acidic Electrolysis of Water.

Cobalt phosphides are an emerging earth-abundant alternative to platinum-group-metal-based electrocatalysts for the hydrogen evolution reaction (HER). Yet, their stability is inferior to platinum and compromises the large-scale applicability of CoP in water electrolyzers. In the present study, we employed flat, thin CoP electrodes prepared through the thermal phosphidation (PH) of CoO films made by plasma-enhanced atomic layer deposition to evaluate their stability in acidic water electrolysis by using a multi-technique approach.

An Active Alkali-Exchanged Faujasite Catalyst for -Xylene Production via the One-Pot Diels-Alder Cycloaddition/Dehydration Reaction of 2,5-Dimethylfuran with Ethylene.

The one-pot Diels-Alder cycloaddition (DAC)/dehydration (D) tandem reaction between 2,5-dimethylfuran and ethylene is a potent pathway toward biomass-derived -xylene. In this work, we present a cheap and active low-silica potassium-exchanged faujasite (KY, Si/Al = 2.6) catalyst.

Confined Carbon Mediating Dehydroaromatization of Methane over Mo/ZSM-5.

Non-oxidative dehydroaromatization of methane (MDA) is a promising catalytic process for direct valorization of natural gas to liquid hydrocarbons. The application of this reaction in practical technology is hindered by a lack of understanding about the mechanism and nature of the active sites in benchmark zeolite-based Mo/ZSM-5 catalysts, which precludes the solution of problems such as rapid catalyst deactivation. By applying spectroscopy and microscopy, it is shown that the active centers in Mo/ZSM-5 are partially reduced single-atom Mo sites stabilized by the zeolite framework.

Multi-site Cooperativity in Alkali-Metal-Exchanged Faujasites for the Production of Biomass-Derived Aromatics.

The catalytic Diels-Alder cycloaddition-dehydration (DACD) reaction of furanics with ethylene is a promising route to bio-derived aromatics. The reaction can be catalyzed by alkali-metal-exchanged faujasites. Herein, the results of periodic DFT calculations based on accurate structural models of alkali-metal-exchanged zeolites are presented, revealing the fundamental roles that confinement and the nature of the exchangeable cations in zeolite micropores have in the performance of faujasite-based catalysts in the DACD reaction.

Establishing hierarchy: the chain of events leading to the formation of silicalite-1 nanosheets.

In applying a multi-scale spectroscopic and computational approach, we demonstrate that the synthesis of stacked zeolite silicalite-1 nanosheets, in the presence of a long-tail diquaternary ammonium salt surfactant, proceeds through a pre-organised phase in the condensed state. small-angle X-ray scattering, coupled to paracrystalline theory, and backed by electron microscopy, shows that this phase establishes its meso-scale order within the first five hours of hydrothermal synthesis. vibrational and solid-state NMR spectroscopy reveal that this meso-shaped architecture already contains some elementary zeolitic features.

Fluoride-assisted synthesis of bimodal microporous SSZ-13 zeolite.

The presence of small amount of fluoride in alkaline hydrothermal synthesis of SSZ-13 zeolite yields bimodal microporous particles with substantially improved performance in the methanol-to-olefins (MTO) reaction. Hydrocarbon uptake measurements and fluorescence microspectroscopy of spent catalysts demonstrate enhanced diffusion through micropores at the grain boundaries of nanocrystals running through the zeolite particles. Fluoride-assisted SSZ-13 synthesis is a cheap and scalable approach to optimize the performance of MTO zeolite catalysts.

Synthesis of hierarchical zeolites using an inexpensive mono-quaternary ammonium surfactant as mesoporogen.

A simple amphiphilic surfactant containing a mono-quaternary ammonium head group (N-methylpiperidine) is effective in imparting substantial mesoporosity during synthesis of SSZ-13 and ZSM-5 zeolites. Highly mesoporous SSZ-13 prepared in this manner shows greatly improved catalytic performance in the methanol-to-olefins reaction compared to bulk SSZ-13.