Mesoporous MFI Zeolite Nanosponge as a High-Performance Catalyst in the Pechmann Condensation Reaction

A zeolite nanosponge possessing <b>MFI</b> framework type was hydrothermally prepared by a seed-assisted synthesis method using C₂₂H₄₅–N⁺(CH₃)₂–C₆H₁₂–N⁺(CH₃)₂–C₆H₁₃ as a structure-directing agent. The nanosponge morphology was composed of a three-dimensional disordered network of <b>MFI</b> nanolayers with 2.5 nm thickness supporting each other. Catalytic performance of the <b>MFI</b> nanosponge was investigated in the Pechmann condensation of bulky reactants (pyrogallol and resorcinol) with ethyl acetoacetate and compared with conventional zeolites <b>MFI</b>, <b>BEA</b>, and USY) and also layered <b>MFI</b>, pillared <b>MFI</b>, and self-pillared <b>MFI</b>. The investigation revealed outstanding catalytic performance of the <b>MFI</b> nanosponge, which can be attributed to the contribution of strong acid sites located on the external surfaces accessible for the reaction of bulky reactants

Adsorption and Diffusion of C₁ to C₄ Alkanes in Dual-Porosity Zeolites by Molecular Simulations

We employ grand canonical Monte Carlo and molecular dynamics simulations to systematically study the adsorption and diffusion of C₁ to C₄ alkanes in hierarchical ZSM-5 zeolite with micropores (∼1 nm) and mesopores (>2 nm). The zeolite is characterized by a large surface area of active sites on the microporous scale with high permeability and access to the active sites, which arises from the enhanced transport at the mesoporous scale. We model this zeolite as a microporous Na⁺-exchanged alumino-sillicate zeolite ZSM-5/35 (Si/Al = 35) in which cylindrical mesopores with a diameter of 4 nm have been built by deleting atoms accordingly. We use the TraPPE and Vujić–Lyubartsev force fields along with the Lorentz–Berthelot combining rules to describe adsorbate–adsorbate and adsorbate–adsorbent interactions. The performance of the force fields is assessed by comparing against experimental single-component adsorption isotherms of methane and ethane in microporous ZSM-5/35, which we measured as part of this work. We compare the adsorption isotherms and diffusivities of the adsorbed alkanes in the dual-porosity zeolite with those in microporous ZSM-5/35 and discern the specific behavior at each porosity scale on the overall adsorption, self-diffusion, and transport behavior in zeolites with dual micro/mesoporosities

Ru-Based Complexes with Quaternary Ammonium Tags Immobilized on Mesoporous Silica as Olefin Metathesis Catalysts

Ruthenium olefin metathesis catalysts bearing a polar quaternary ammonium group in N-heterocyclic ligand were immobilized on silica and siliceous mesoporous molecular sieves with different pore sizes (SBA-15 and MCM-41). The activity of the heterogeneous catalysts was found to increase with an increase in pore size of the support used, with the best results observed for SBA-15-supported catalyst. The influence of reaction conditions (temperature, solvent, catalyst, and substrate concentration) on the efficiency of new heterogeneous catalysts was established. A significant influence of the counterion present in the ruthenium complex on the activity of immobilized catalysts was also found: those derived from chloride containing ion exhibited the highest activity. High activity in ring-closing metathesis of substrates as citronellene, 1,7-octadiene, and diallyl compounds as well as in cross-metathesis of unsaturated aliphatic compounds with methyl acrylate was observed under optimized conditions. In some cases, heterogenization led to catalysts with efficiency higher than those observed for corresponding homogeneous complexes

Microporous Lead–Organic Framework for Selective CO₂ Adsorption and Heterogeneous Catalysis

A novel microporous metal–organic framework, {[Pb₄(μ₈-MTB)₂(H₂O)₄]·5DMF·H₂O}_<i>n</i> (<b>1</b>; MTB = methanetetrabenzoate and DMF = <i>N</i>,<i>N</i>′-dimethylformamide), was successfully synthesized by a solvothermal reaction and structurally characterized by single-crystal X-ray diffraction. The framework exhibits a unique tetranuclear [Pb₄(μ₃-COO)­(μ₂-COO)₆(COO)­(H₂O)₄] secondary building unit (SBU). The combination of the SBU with the tetrahedral symmetry of MTB results in a three-dimensional network structure, with one-dimensional jarlike cavities having sizes of about 14.98 × 7.88 and 14.98 × 13.17 Ų and propagating along the <i>c</i> axis. Due to the presence of four coordinately unsaturated sites per one metal cluster, an activated form of compound <b>1</b> (i.e., desolvated form denoted as <b>1′</b>) was tested in gas adsorption and catalytic experiments. The studies of gas sorption revealed that <b>1′</b> exhibits a surface area (Brunauer–Emmett–Teller) of 980 m²·g^–1. This value is the highest reported for any compound from the MTB group. Interactions of carbon dioxide (CO₂) molecules with the framework, confirmed by density functional theory calculations, resulted in high CO₂ uptake and significant selectivity of CO₂ adsorption with respect to methane (CH₄) and dinitrogen (N₂) when measured from atmospheric pressure to 21 bar. The high selectivity of CO₂ over N₂ is mostly important for capturing CO₂ from the atmosphere in attempts to decrease the greenhouse effect. Moreover, compound <b>1′</b> was tested as a heterogeneous catalyst in Knoevenagel condensation of active methylene compounds with aldehydes. Excellent catalytic conversion and selectivity in the condensation of benzaldehyde and cyclohexanecarbaldehyde with malononitrile was observed, which suggests that accessible lead­(II) sites play an important role in the heterogeneous catalytic process