One-Step Synthesis of Highly Efficient Nanocatalysts on the Supports with Hierarchical Pores Using Porous Ionic Liquid-Water Gel

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

A COF template-derived mesoporous CeO2-supported Au nanoparticles catalyst for the oxidative esterification of benzaldehydes and benzyl alcohols

The direct oxidative esterification of benzaldehydes and benzyl alcohols to high value-added aromatic esters under mild and green reaction conditions is significant in the fine chemical industry. The accurate design of catalysts with high catalytic performance is crucial for this process. Herein, 2,4,6-trimethylpyridine, benzoic anhydride, and terephthalaldehyde were used to prepare a covalent organic framework (COF) material, which was then used as a template to construct a mesoporous CeO2-supported Au nanoparticles catalyst. The obtained Au@CeO2 catalyst was thoroughly characterized, and it possessed a mesoporous structure with a high surface area. Meanwhile, the as-prepared Au@CeO2 exhibited excellent catalytic performance in the oxidative esterification of benzaldehydes and benzyl alcohols with methanol, affording the corresponding aromatic esters under mild and green reaction conditions. Furthermore, the Au@CeO2 catalyst could also be recycled. Therefore, this study provides a green and sustainable pathway for the synthesis of high-value-added esters through a direct oxidative esterification strategy.

Ionic Liquids Functionalized MOFs for Adsorption

Metal-organic frameworks (MOFs) and ionic liquids (ILs) represent promising materials for adsorption separation. ILs incorporated into MOF materials (denoted as IL/MOF composites) have been developed, and IL/MOF composites combine the advantages of MOFs and ILs to achieve enhanced performance in the adsorption-based separation of fluid mixtures. The designed different ILs are introduced into the various MOFs to tailor their functional properties, which affect the optimal adsorptive separation performance. In this Perspective, the rational fabrication of IL/MOF composites is presented, and their functional properties are demonstrated. This paper provides a critical overview of an emergent class of materials termed IL/MOF composites as well as the recent advances in the applications of IL/MOF composites as adsorbents or membranes in fluid separation. Furthermore, the applications of IL/MOF in adsorptive gas separations (CO2 capture from flue gas, natural gas purification, separation of acetylene and ethylene, indoor pollutants removal) and liquid separations (separation of bioactive components, organic-contaminant removal, adsorptive desulfurization, radionuclide removal) are discussed. Finally, the existing challenges of IL/MOF are highlighted, and an appropriate design strategy direction for the effective exploration of new IL/MOF adsorptive materials is proposed.

Hierarchical porous metal–organic gels and derived materials: from fundamentals to potential applications

This review summarizes recent progress in the development and applications of metal–organic gels (MOGs) and their hybrids and derivatives dividing them into subclasses and discussing their synthesis, design and structure–property relationship.

Integration of mesopores and crystal defects in metal-organic frameworks via templated electrosynthesis

Incorporation of mesopores and active sites into metal-organic framework (MOF) materials to uncover new efficient catalysts is a highly desirable but challenging task. We report the first example of a mesoporous MOF obtained by templated electrosynthesis using an ionic liquid as both electrolyte and template. The mesoporous Cu(II)-MOF MFM-100 has been synthesised in 100 seconds at room temperature, and this material incorporates crystal defects with uncoupled Cu(II) centres as evidenced by confocal fluorescence microscopy and electron paramagnetic resonance spectroscopy. MFM-100 prepared in this way shows exceptional catalytic activity for the aerobic oxidation of alcohols to produce aldehydes in near quantitative yield and selectivity under mild conditions, as well as having excellent stability and reusability over repeated cycles. The catalyst-substrate binding interactions have been probed by inelastic neutron scattering. This study offers a simple strategy to create mesopores and active sites simultaneously via electrochemical formation of crystal defects to promote efficient catalysis using MOFs.

Incorporating mesopores and active sites into metal-organic framework materials has proven advantageous for their catalytic application, but remains challenging to achieve. Here the authors obtain mesoporous, defect-rich metal-organic frameworks through templated electrosynthesis using ionic liquids as both electrolyte and template.

Birch-Type Reduction of Arenes in 2-Propanol Catalyzed by Zero-Valent Iron and Platinum on Carbon

Catalytic arene reduction was effectively realized by heating in 2-propanol/water in the presence of Pt on carbon (Pt/C) and metallic Fe. 2-Propanol acted as a hydrogen source, obviating the need for flammable (and hence, dangerous and hard-to-handle) hydrogen gas, while metallic Fe acted as an essential co-catalyst to promote reduction. The chemical states of Pt and Fe in the reaction mixture were determined by X-ray absorption near-edge structure analysis, and the obtained results were used to suggest a plausible reaction mechanism, implying that catalytic reduction involved Pt- and Fe-mediated single-electron transfer and the dehydrogenation of 2-propanol.

Pickering Emulsion-Derived Liquid-Solid Hybrid Catalyst for Bridging Homogeneous and Heterogeneous Catalysis

We describe a novel method to prepare a liquid-solid hybrid catalyst via interfacial growth of a porous silica crust around Pickering emulsion droplets, which allowed us to overcome the current limitations of both homogeneous and heterogeneous catalysts. The inner micron-scaled liquid (for example, ionic liquids) pool of the resultant catalyst can host free homogeneous molecular catalysts or enzymes to create a true homogeneous catalysis environment. The porous silica crust of the hybrid catalyst has excellent stability, which makes it amenable to packing directly in fixed-bed reactors for continuous flow catalysis. As a proof of concept, the enzymatic kinetic resolution of racemic alcohols, Cr^III(salen) complex-catalyzed asymmetric ring opening of epoxides and Pd-catalyzed Tsuji-Trost allylic substitution reactions were used to verify the generality and versatility of our strategy for bridging homogeneous and heterogeneous catalysis. The hybrid catalyst-based continuous flow system exhibited a 1.6∼16-fold enhancement in activity relative to homogeneous counterparts even over 1500 h, and the afforded enantioselectivities were completely equal to those obtained in the homogeneous counterpart systems. Interestingly, the catalytic efficiency can be tuned through rational engineering of the porous crust and the dimensions of the liquid pool, resulting in features of an innovatively designed catalyst. This contribution provides a new method to design efficient catalysts that can bridge the conceptual and technical gaps between homogeneous and heterogeneous catalysis.

Green chemical engineering in China

In China, the rapid development greatly promotes the national economic power and living standard but also inevitably brings a series of environmental problems. In order to resolve these problems fundamentally, Chinese scientists have been undertaking research in the area of green chemical engineering (GCE) for many years and achieved great progresses. In this paper, we reviewed the research progresses related to GCE in China and screened four typical topics related to the Chinese resources characteristics and environmental requirements, i.e. ionic liquids and their applications, biomass utilization and bio-based materials/products, green solvent-mediated extraction technologies, and cold plasmas for coal conversion. Afterwards, the perspectives and development tendencies of GCE were proposed, and the challenges which will be faced while developing available industrial technologies in China were mentioned.

A copper(ii) metal-organic hydrogel as a multifunctional precatalyst for CuAAC reactions and chemical fixation of CO2 under solvent free conditions

A copper(ii) metal-organic hydrogel has been synthesised and characterised. This hydrogel is an efficient, reusable precatalyst for CuAAC reactions and chemical fixation of CO₂ under solvent free conditions.

Single-Site AuI Catalyst for Silane Oxidation with Water

Single-site Au anchored on mpg-C₃ N₄ (519 ppm Au loading) is developed as a highly active, selective, and stable catalyst for the oxidation of silanes with water with a turnover frequency as high as 50 200 h^-1 , far exceeding most known catalysts based on total gold content. Other hydrosilanes bearing unsaturated functional groups also lead to corresponding silanols under mild reaction conditions without formation of any side products in good or excellent yields. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Au atoms stabilized by mpg-C₃ N₄ . The coordination of the catalytically active Au^I by three nitrogen or carbon atoms in the tri-s-triazine repeating units not only prevents the Au atoms from aggregation, but also renders the surface Au^I highly active, which is completely different than homogeneous Au^I species.

A route to support Pt sub-nanoparticles on TiO2 and catalytic hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline at room temperature

We report a method to support Pt sub-nanoparticles on TiO₂.

Ionic Liquid/Metal-Organic Framework Composites: From Synthesis to Applications

Metal-organic frameworks (MOFs) have been widely studied for different applications owing to their fascinating properties such as large surface areas, high porosities, tunable pore sizes, and acceptable thermal and chemical stabilities. Ionic liquids (ILs) have been recently incorporated into the pores of MOFs as cavity occupants to change the physicochemical properties and gas affinities of MOFs. Several recent studies have shown that IL/MOF composites show superior performances compared with pristine MOFs in various fields, such as gas storage, adsorption and membrane-based gas separation, catalysis, and ionic conductivity. In this review, we address the recent advances in syntheses of IL/MOF composites and provide a comprehensive overview of their applications. Opportunities and challenges of using IL/MOF composites in many applications are reviewed and the requirements for the utilization of these composite materials in real industrial processes are discussed to define the future directions in this field.

Porous Ionic Polymers as a Robust and Efficient Platform for Capture and Chemical Fixation of Atmospheric CO2

Direct use of atmospheric CO₂ as a C₁ source to synthesize high-value chemicals through environmentally benign processes is of great interest, yet challenging. Porous heterogeneous catalysts that are capable of simultaneously capturing and converting CO₂ are promising candidates for such applications. Herein, a family of organic ionic polymers with nanoporous structure, large surface area, strong affinity for CO₂ , and very high density of catalytic active sites (halide ions) was synthesized through the free-radical polymerization of vinylfunctionalized quaternary phosphonium salts. The resultant porous ionic polymers (PIPs) exhibit excellent activities in the cycloaddition of epoxides with atmospheric CO₂ , outperforming the corresponding soluble phosphonium salt analogues and ranking among the highest of known metal-free catalytic systems. The high CO₂ uptake capacity of the PIPs facilitates the enrichment of CO₂ molecules around the catalytic centers, thereby benefiting its conversion. We have demonstrated for the first time that atmospheric CO₂ can be directly converted to cyclic carbonates at room temperature using a heterogeneous catalytic system under metal-solvent free conditions. Moreover, the catalysts proved to be robust and fully recyclable, demonstrating promising potential for practical utilization for the chemical fixation of CO₂ . Our work thereby paves a way to the advance of PIPs as a new type of platform for capture and conversion of CO₂ .

Anion exchange: a novel way of preparing hierarchical porous structure in poly(ionic liquid)s

The exchange of bulky salicylate and its dimers/clusters in PILs by other smaller anions increased specific surface area and fabricated a hierarchical porous structure.

Influence of the Headgroup of Azolium-Based Lipids on Their Biophysical Properties and Cytotoxicity

A series of (un-)charged NHC derivatives bearing two pentadecyl chains in the backbone was studied in detail to find cooperative effects between the membrane and the NHC derivative. The tendency to show lipid-like behavior is dependent on the properties of the NHC derivative headgroup, which can be modified on demand. The surface activity was investigated by film balance measurements, epifluorescence microscopy, and differential scanning calorimetry. Additionally the cytotoxicity was evaluated against different cell lines such as eukaryotic tumor cell lines. These novel lipid-like NHC derivatives offer a broad spectrum for biological applications.

Synthesis of hierarchical porous β-FeOOH catalysts in ionic liquid/water/CH2Cl2 ionogels

The ionic liquid/water/CH2Cl2 ionogels were created for the first time, which were used to synthesize hierarchical porous β-FeOOH catalysts. The pore property and crystallinity could be tuned by the CH2Cl2 content in the ionogels. The as-synthesized β-FeOOH catalysts exhibited very high activity and stability for oxidation of benzylic carbons.

Chemoselective dehydrogenative esterification of aldehydes and alcohols with a dimeric rhodium(ii) catalyst

A dimeric rhodium(ii) complex catalyses the chemoselective dehydrogenative esterification of aldehydes and alcohols.

Dehydrogenative cross-coupling of aldehydes with alcohols as well as dehydrogentive cross-coupling of primary alcohols to produce esters have been developed using a Rh-terpyridine catalyst. The catalyst demonstrates broad substrate scope and good functional group tolerance, affording esters highly selectively. The high chemoselectivity of the catalyst stems from its preference for dehydrogenation of benzylic alcohols over aliphatic ones. Preliminary mechanistic studies suggest that the active catalyst is a dimeric Rh(ii) species, operating via a mechanism involving metal–base–metal cooperativity.

Synthesis of Functional Nanomaterials in Ionic Liquids

Utilization of ionic liquids (ILs) in material synthesis is a promising field. The unusual properties of ILs provide new opportunities for the design of functional materials, and much excellent work has been reported. Here, the progress in material design and synthesis using ILs, especially nanomaterials, is discussed, including the unitization of ILs as synthetic media, templates, precursors, or components in the synthesis of various categories of nanomaterials. The challenges and opportunities in this interesting and rapid developing area are also discussed.

Gold nanoparticles encapsulated in hierarchical porous polycarbazole: preparation and application in catalytic reduction

AuNPs/porous polycarbazole composites with hierarchical pores exhibit high porosity and efficient catalytic reduction.

Highly efficient electrochemical reduction of CO2 to CH4 in an ionic liquid using a metal-organic framework cathode

Highly efficient electrochemical reduction of CO2 to CH4 is of great importance, but is challenging. Herein, Zn-1,3,5-benzenetricarboxylic acid metal-organic frameworks (Zn-BTC MOFs) deposited on carbon paper (CP) were used as cathodes in electrochemical reduction of CO2 using ionic liquids (ILs) as the electrolytes, which was the first work on combination of a MOF electrode and an pure IL electrolyte in the electrochemical reduction of CO2. It was found that the efficiency of the reaction depended strongly on the morphology of the Zn-MOFs. Compared with the commonly used metal electrodes, the electrochemical reaction showed much higher selectivity to CH4 and current density, and the overpotentials for CH4 is much lower. The excellent combination of the MOF cathodes and ILs opens a way for reduction of CO2 to CH4 effectively.

Formation of large nanodomains in liquid solutions near the phase boundary

Large nanodomains were formed in liquid solutions near the phase separation point where the size of nanodomains increased dramatically.

Surface passivation of titanium dioxide via an electropolymerization method to improve the performance of dye-sensitized solar cells

We introduce an electrochemical method for insulating and passivation open areas of a nanoporous TiO₂ in dye-sensitized solar cells, which can effectively decrease the recombination rate of electrons.

Development Trends in Porous Adsorbents for Carbon Capture

Accumulation of greenhouse gases especially CO2 in the atmosphere leading to global warming with undesirable climate changes has been a serious global concern. Major power generation in the world is from coal based power plants. Carbon capture through pre- and post- combustion technologies with various technical options like adsorption, absorption, membrane separations, and chemical looping combustion with and without oxygen uncoupling have received considerable attention of researchers, environmentalists and the stake holders. Carbon capture from flue gases can be achieved with micro and meso porous adsorbents. This review covers carbonaceous (organic and metal organic frameworks) and noncarbonaceous (inorganic) porous adsorbents for CO2 adsorption at different process conditions and pore sizes. Focus is also given to noncarbonaceous micro and meso porous adsorbents in chemical looping combustion involving insitu CO2 capture at high temperature (>400 °C). Adsorption mechanisms, material characteristics, and synthesis methods are discussed. Attention is given to isosteric heats and characterization techniques. The options to enhance the techno-economic viability of carbon capture techniques by integrating with CO2 utilization to produce industrially important chemicals like ammonia and urea are analyzed. From the reader's perspective, for different classes of materials, each section has been summarized in the form of tables or figures to get a quick glance of the developments.

Transformation of atmospheric CO2 catalyzed by protic ionic liquids: efficient synthesis of 2-oxazolidinones

Protic ionic liquids (PILs), such as 1,8-diazabicyclo[5.4.0]-7-undecenium 2-methylimidazolide [DBUH][MIm], can catalyze the reaction of atmospheric CO2 with a broad range of propargylic amines to form the corresponding 2-oxazolidinones. The products are formed in high yields under mild, metal-free conditions. The cheaper and greener PILs can be easily recycled and reused at least five times without a decrease in the catalytic activity and selectivity. A reaction mechanism was proposed on the basis of a detailed DFT study which indicates that both the cation and anion of the PIL play key synergistic roles in accelerating the reaction.

Noncrystalline structure of Ni-P nanoparticles prepared by liquid pulse discharge

Noncrystalline nickel phosphide (Ni-P) nanoparticles have drawn great attention due to their high potential as catalysts. However, the structure of noncrystalline Ni-P nanoparticles is still unknown, which may shed light on explaining the catalysis mechanism of the Ni-P nanoparticles. In this paper, noncrystalline Ni-P nanoparticles were synthesized. Their morphology, particle size, element contents, local atomic structures, as well as the catalysis in the thermal decomposition of ammonium perchlorate were studied. The results demonstrate that the as-prepared Ni-P nanoparticles are spherical with an average diameter of about 13.5 nm. The Ni and P contents are, respectively, 78.15% and 21.85%. The noncrystalline nature of the as-prepared Ni-P nanoparticles can be attributed to cross-linkage between P-doping f.c.c.-like Ni centers and Ni3P-like P centers. The locally ordered Ni centers and P centers are the nuclei sites, which can explain well the origin of initial nuclei to form the crystalline phases after high-temperature annealing. The starting temperature of high-temperature decomposition of ammonium perchlorate was found having a significant decrease in the presence of the noncrystalline Ni-P nanoparticles. Therefore, the as-prepared noncrystalline Ni-P nanoparticles can be used as a potential catalyst in the thermal decomposition of ammonium perchlorate.