Double-shell microcapsules with spatially arranged Au nanoparticles and single Zn atoms for tandem synthesis of cyclic carbonates

Hollow Nanoreactors Unlock New Possibilities for Persulfate-Based Advanced Oxidation Processes

As a novel type of catalytic material, hollow nanoreactors are expected to bring new development opportunities in the field of persulfate-based advanced oxidation processes due to their peculiar void-confinement, spatial compartmentation, and size-sieving effects. For such materials, however, further clarification on basic concepts and construction strategies, as well as a discussion of the inherent correlation between structure and catalytic activity are still required. In this context, this review aims to provide a state-of-the-art overview of hollow nanoreactors for activating persulfate. Initially, hollow nanoreactors are classified according to the constituent components of the shell structure and their dimensionality. Subsequently, the different construction strategies of hollow nanoreactors are described in detail, while common synthesis methods for these construction strategies are outlined. Furthermore, the most representative advantages of hollow nanoreactors are summarized, and their intrinsic connections to the nanoreactor structure are elucidated. Finally, the challenges and future prospects of hollow nanoreactors are presented.

Atomically Dispersed Metal Catalysts for the Conversion of CO2 into High-Value C2+ Chemicals

The conversion of carbon dioxide (CO2) into value-added chemicals with two or more carbons (C2+) is a promising strategy that cannot only mitigate anthropogenic CO2 emissions but also reduce the excessive dependence on fossil feedstocks. In recent years, atomically dispersed metal catalysts (ADCs), including single-atom catalysts (SACs), dual-atom catalysts (DACs), and single-cluster catalysts (SCCs), emerged as attractive candidates for CO2 fixation reactions due to their unique properties, such as the maximum utilization of active sites, tunable electronic structure, the efficient elucidation of catalytic mechanism, etc. This review provides an overview of significant progress in the synthesis and characterization of ADCs utilized in photocatalytic, electrocatalytic, and thermocatalytic conversion of CO2 toward high-value C2+ compounds. To provide insights for designing efficient ADCs toward the C2+ chemical synthesis originating from CO2, the key factors that influence the catalytic activity and selectivity are highlighted. Finally, the relevant challenges and opportunities are discussed to inspire new ideas for the generation of CO2-based C2+ products over ADCs.

A Hierarchical Metal-Organic Framework Composite Aerogel Catalyst Containing Integrated Acid, Base, and Metal Sites for the One-Pot Catalytic Synthesis of Cyclic Carbonates

Catalysis has played a decisive role in the development of unique chemical reactions to produce important chemicals. However, conventional stepwise synthetic routes that rely on individual catalysts to promote each step often suffer from ponderous processes for the isolation of intermediates that result in massive material losses and large economic expenditures. In addition, traditional powder forms of these catalysts suffer from poor processability and recoverability. Herein, we designed and prepared a hierarchical metal-organic framework (MOF) composite monolithic catalyst IL-Au@UiO-66-NH2/CMC that contains integrated acid (Zr4+), base (ionic liquid (IL)), and metal sites (Au nanoparticles (NPs)) to promote the one-pot preparation of cyclic carbonates from styrene derivatives and CO2. Highly dispersed Au NPs, IL 1-aminoethyl-3-methylimidazolium bromide ([C2NH2 MIM] [Br]), and MOF-positioned Lewis acid sites within this composite aerogel are separately responsible for catalyzing selective epoxidation of the styrene derivatives and the subsequent cycloaddition reaction of CO2 with intermediate styrene oxides. Importantly, inclusion of the imidazolium-based IL effectively modulates the size and chemical microenvironment of the Au NPs via electrostatic protection, leading to catalyst stability and its selective oxidation of styrene. Benefiting from the rapid mass transfer and high exposure of active sites within the pore-rich hierarchical nanostructure, IL-Au@UiO-66-NH2/CMC promotes high conversion (90.5%) of the styrene and selectivity (80.5%) for styrene carbonate (SC) formation in the one-pot process, a performance level that far exceeds those of related catalysts containing only Au NPs or IL (the selectivity of SC < 42%). Furthermore, the composite aerogel catalyst can be readily separated and recycled at least five times without a remarkable loss of activity and selectivity. The controllable integration of various active components in the hierarchical MOF composite aerogel herein should serve as the foundation for the design of multifunctional monolithic catalysts for other valuable tandem processes.

Regulation of frustrated Lewis pairs on CeO2 facilitates tandem transformation of styrene and CO2

The frustrated Lewis pair (FLP) site of (Ce, Ce)-O on the CeO2(110) surface undergoes reconstruction to form (La, Ce)-O upon La-doping. The FLP site of (La, Ce)-O with the tailored local Lewis acid-base property and increased spatial distance between the Lewis acid and base facilitates the tandem transformation of styrene and CO2 through the weakened adsorption of CO2 while maintaining activation.

Self-assembled mononuclear complexes: open metal sites and inverse dimension-dependent catalytic activity for the Knoevenagel condensation and CO2 cycloaddition

To lessen the greenhouse effect, measures such as improving the recovery of crude oil and converting carbon dioxide (CO₂) into valuable chemicals are necessary to create a sustainable low-carbon future. To this end, the development of efficient new oil-displacing agents and CO₂ conversion has aroused great interest in both academia and industry. The Knoevenagel condensation and CO₂ cycloaddition are the key reactions to solve the above problems. Four Cu- or Zn-based molecular complexes built from different ligands possessing hydrophilic-hydrophobic layers and different dimensionalities were chosen as solid catalysts for this study. Structural analysis revealed the presence of hydrophilic-hydrophobic layers and open metal sites in the low-dimensional complexes. To obtain deep insight into the reaction mechanism, first-principles density functional theory (DFT) calculations were carried out. These calculations confirmed that in the Knoevenagel condensation reaction, the final formation of benzylidenemalononitrile is the rate-determining step (an energy barrier (ΔE) value of 73.2 kJ mol^-1). The zero-dimensional (0D) Cu molecular complex with unsaturated metal centers, hydrophilic and hydrophobic layers, exhibited higher catalytic activity (yield: 100%, temperature: room temperature, and time: 2 h) compared with one- and two-dimensional Cu complexes. In the presence of a 0D Zn complex co-catalyzed with Br^- in the CO₂ cycloaddition reaction, the ΔE value reduces to 35.5 kJ mol^-1 for the ring opening of styrene oxide (SO), which is significantly lower than Br^- catalyzed (80.9 kJ mol^-1) reactions. The roles of unsaturated metal centers, hydrophilic-hydrophobic layers and dimensionality in the Knoevenagel condensation and CO₂ cycloaddition were explained in the results of structure-activity relationships.

Recent Achievements in the Synthesis of Cyclic Carbonates from Olefins and CO2: The Rational Design of the Homogeneous and Heterogeneous Catalytic System

With the consumption of fossil fuels, the level of CO2 in the atmosphere is growing rapidly, which leads to global warming. Hence, the chemical conversion of CO2 into high value-added products is one of the most important approaches to reducing CO2 emissions. Due to being simple, inexpensive and environmentally friendly, the direct synthesis of cyclic carbonates from olefins and CO2 is a promising project for industrial application. In this review, we discuss the design of the homogeneous and heterogeneous catalytic system for the synthesis of cyclic carbonates from the reaction of olefins and CO2. Usually, the catalyst contains the epoxidation active site and the cycloaddition active site, which could achieve the oxidation of oleifins and the CO2-insert, respectively. This review will provide a comprehensive overview of the direct synthesis of cyclic carbonates from olefins and CO2 catalyzed by homogeneous and heterogeneous catalysts. The focus mainly lies on the rational fabrication of multifunctional catalysts, and provides a new perspective for the design of catalysts.

Core-shell TiO2-x-CuyO microspheres for photogeneration of cyclic carbonates under simulated sunlight

Propylene carbonates are important organic solvents and feedstocks for different applications, including synthesis of polymers and Li-batteries. The generation of propylene carbonate utilising anthropogenic CO₂ and renewable solar energy offers an alternative sustainable process with a closed loop carbon cycle. The development of microstructured photocatalysts with desired properties, including high degree of product selectivity, wide range of optical properties, and maximised conversion yield, plays an important role for effective production of propylene carbonate from CO₂. A hierachical hollow core with a double shell of TiO_2-x-Cu₂O-CuO was fabricated using the versatile solvothermal-microwave synthesis method. The fabricated sample revealed effective cascading of photogenerated electrons and holes that promoted the conversion of propylene carbonate (i.e., 1.6 wt%) under 1 Sun irradiation.