Interface-Active Metal Organic Frameworks for Knoevenagel Condensations in Water

Insights into the Structure-Property-Activity Relationship of Zeolitic Imidazolate Frameworks for Acid-Base Catalysis

Zeolitic imidazolate frameworks (ZIFs) have been extensively examined for their potential in acid-base catalysis. Many studies have demonstrated that ZIFs possess unique structural and physicochemical properties that allow them to demonstrate high activity and yield products with high selectivity. Herein, we highlight the nature of ZIFs in terms of their chemical formulation and the textural, acid-base, and morphological properties that strongly affect their catalytic performance. Our primary focus is the application of spectroscopic methods as instruments for analyzing the nature of active sites because these methods can allow an understanding of unusual catalytic behavior from the perspective of the structure-property-activity relationship. We examine several reactions, such as condensation reactions (the Knoevenagel condensation and Friedländer reactions), the cycloaddition of CO₂ to epoxides, the synthesis of propylene glycol methyl ether from propylene oxide and methanol, and the cascade redox condensation of 2-nitroanilines with benzylamines. These examples illustrate the broad range of potentially promising applications of Zn-ZIFs as heterogeneous catalysts.

High-Performance Heterogeneous Thermocatalysis Caused by Catalyst Wettability Regulation

Catalyst wettability regulation has emerged as an attractive approach for high catalytic performance for the past few years. By introducing appropriate wettability, the molecule diffusion of reactants and products can be enhanced, leading to high activity. Besides this, undesired molecules are isolated for high selectivity of target products and long-term stability of catalyst. Herein, we summarize wettability-induced high-performance heterogeneous thermocatalysis in recent years, including hydrophilicity, hydrophobicity, hybrid hydrophilicity-hydrophobicity, amphiphilicity, and superaerophilicity. Relevant reactions are further classified and described according to the reason for the performance improvement. It should be pointed out that studies of utilizing superaerophilicity to improve heterogeneous thermocatalytic performance have been included for the first time, so this is a comparatively comprehensive review in this field as yet.

Microstructural and rheological investigation of upcycled metal-organic frameworks stabilized Pickering emulsions

HYPOTHESIS

Stabilizing Pickering emulsions with metal-organic frameworks (MOFs) is a known way to incorporate them into hierarchically porous materials. Studies generally focus on their final properties and emulsion microstructures are rarely precisely described. Our hypothesis was that characterizing the microstructural and rheological properties of Pickering emulsions stabilized solely by Al-based MOFs (MIL-96) particles would provide insights into how to control their stability and workability for potential industrial applications.

EXPERIMENTS

MIL-96(Al) particles, obtained from Li-ion battery waste were used to stabilize paraffin-in-water Pickering emulsions. The influence of the formulation parameters (paraffin/water volume ratio and MIL-96(Al) content) were investigated and the emulsions were analysed using optical microscopy, cryo-scanning electron microscopy and rheological measurements.

FINDINGS

MIL-96(Al) efficiently stabilized paraffin-in-water emulsions with up to 80% of internal phase. The emulsions with a low paraffin volume fraction had large droplets and a fluid gel-like texture. The emulsions with higher paraffin volume fractions were more compact and had two-step flow curves. In this system, excess MIL-96(Al) particles aggregated in the continuous phase as flocs interact with particles adsorbed at the paraffin-water interface, creating a secondary network that has to be broken for flow to resume. This behaviour may be interesting to investigate in other MOF-stabilized emulsions.

Imidazole-induced self-assembly of polyoxovanadate cluster organic framework for efficient Knoevenagel condensation under mild conditions

Three new polyoxovanadates have been made, one of them displays highly efficient heterogeneous solvent-free catalytic activity and excellent recyclability in the Knoevenagel condensation at room temperature.

Preparation of a Pickering emulsion by modification of an amine-functionalized graphene oxide surface with organosilane: efficient catalyst for the Knoevenagel condensation of malononitrile with aldehydes at mild temperature

In this study, a series of Pickering emulsions for catalysis of Knoevenagel condensations of malononitrile with aldehydes were prepared by surface modification of amine-functionalized graphene oxide (GO-NH₂) with trimethoxymethylsilane (MTMS).

Two organic–inorganic hybrid polyoxovanadates as reusable catalysts for Knoevenagel condensation

Two novel polyoxovanadates as heterogeneous catalysts have exhibited excellent catalytic properties in the Knoevenagel condensation, especially compound 1's activity is basically maintained after three cycles.

Erratum: Zhang, Y., et al. Interface-Active Metal Organic Frameworks for Knoevenagel Condensations in Water. Catalysts 2018, 8, 315

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