Ion Exchange Resins: Catalyst Recovery and Recycle

Thermo-responsive chiral micelles as recyclable organocatalyst for asymmetric Rauhut-Currier reaction in water

Developing eco-friendly chiral organocatalysts with the combined advantages of homogeneous catalysis and heterogeneous processes is greatly desired. In this work, a family of amphiphilic one-handed helical polyisocyanides bearing phosphine pendants is prepared, which self-assembles into well-defined chiral micelles in water and showed thermo-responsiveness with a cloud point of approximately 38.4 °C. The micelles with abundant phosphine moieties at the interior efficiently catalyze asymmetric cross Rauhut-Currier reaction in water. Various water-insoluble substrates are transferred to target products in high yield with excellent enantioselectivity. The yield and enantiomeric excess (ee) of the product generated in water are up to 90% and 96%, respectively. Meanwhile, the yields of the same R-C reaction catalyzed by the polymer itself in organic solvents is <16%, with an ee < 72%. The homogeneous reaction of the chiral micelles in water turns to heterogeneous at temperatures higher than the cloud point, and the catalyst precipitation facilitates product isolation and catalyst recovery. The polymer catalyst is recycled 10 times while maintaining activity and enantioselectivity.

Recent Advances On Direct Formylation Reactions

Aldehydes serve as the key functional group in organic synthesis and are valuable intermediates. The various advanced methods of direct formylation reactions have been reviewed in this article. Overcoming the drawbacks of the traditional methods of formylation, newer methods involving homo and heterogenous catalysts, one pot reactions, solvent free techniques are elaborated, which can be performed under mild conditions and using inexpensive resources.

Counterion-Mediated Hydrogen Bonding Making Poly(styrenesulfonate)-Based Strong Polyelectrolytes pH-Responsive

Owing to the well-established fact that poly(styrenesulfonate) (PSS)-based strong polyelectrolytes are pH insensitive, their applications in smart materials have thus been severely limited. However, we demonstrate here that counterion-mediated hydrogen bonding (CMHB) makes the PSS brush pH-responsive. With decreasing pH, more hydrogen bonds are formed between the bound hydronium counterions and the sulfonate (-SO3-) groups in the PSS brush. At the microscale, the formation of more hydrogen bonds with decreasing pH leads to a more ordered structure and a larger tilt angle of the -SO3- groups in the PSS brush. On the other hand, a range of important physicochemical properties of the PSS brush, including hydration, stiffness, wettability, and adhesion, are responsive to pH, induced by the effect of CMHB on the PSS brush. Our work reveals a clear structure-property relationship for the pH-responsive PSS brush. This work not only provides a new understanding of the fundamental properties of the PSS brush but also greatly extends the applications of PSS-based strong polyelectrolytes.

Sulfation of Birch Wood Microcrystalline Cellulose with Sulfamic Acid Using Ion-Exchange Resins as Catalysts

Cellulose sulfates are important biologically active substances with a wide range of useful properties. The development of new methods for the production of cellulose sulfates is an urgent task. In this work, we investigated ion-exchange resins as catalysts for the sulfation of cellulose with sulfamic acid. It has been shown that water-insoluble sulfated reaction products are formed in high yield in the presence of anion exchangers, while water-soluble products are formed in the presence of cation exchangers. The most effective catalyst is Amberlite IR 120. According to gel permeation chromatography, it was shown that the samples sulfated in the presence of the catalysts KU-2-8, Purolit s390 plus, and AN-31 SO₄^2- underwent the greatest degradation. The molecular weight destribution profiles of these samples are noticeably shifted to the left towards low-molecular-weight compounds with an increase in fractions in the regions Mw ~2.100 g/mol and ~3.500 g/mol, indicating the growth of microcrystalline cellulose depolymerization products. The introduction of a sulfate group into the cellulose molecule is confirmed using FTIR spectroscopy by the appearance of absorption bands at 1245-1252 cm^-1 and 800-809 cm^-1, which correspond to the vibrations of the sulfate group. According to X-ray diffraction data, amorphization of the crystalline structure of cellulose is observed during sulfation. Thermal analysis has shown that with an increase in the content of sulfate groups in cellulose derivatives, thermal stability decreases.

Selenium-enriched plant foods: Selenium accumulation, speciation, and health functionality

Selenium (Se) is an essential element for maintaining human health. The biological effects and toxicity of Se compounds in humans are related to their chemical forms and consumption doses. In general, organic Se species, including selenoamino acids such as selenomethionine (SeMet), selenocystine (SeCys₂), and Se-methylselenocysteine (MSC), could provide greater bioactivities with less toxicity compared to those inorganics including selenite (Se IV) and selenate (Se VI). Plants are vital sources of organic Se because they can accumulate inorganic Se or metabolites and store them as organic Se forms. Therefore, Se-enriched plants could be applied as human food to reduce deficiency problems and deliver health benefits. This review describes the recent studies on the enrichment of Se-containing plants in particular Se accumulation and speciation, their functional properties related to human health, and future perspectives for developing Se-enriched foods. Generally, Se's concentration and chemical forms in plants are determined by the accumulation ability of plant species. Brassica family and cereal grains have excessive accumulation capacity and store major organic Se compounds in their cells compared to other plants. The biological properties of Se-enriched plants, including antioxidant, anti-diabetes, and anticancer activities, have significantly presented in both in vitro cell culture models and in vivo animal assays. Comparatively, fewer human clinical trials are available. Scientific investigations on the functional health properties of Se-enriched edible plants in humans are essential to achieve in-depth information supporting the value of Se-enriched food to humans.

Screening, synthesis optimization, and scaling-up of phytopathogen antifungals derived from natural hydroxycinnamic acids

A simple screening methodology was employed to correlate the structures of hydroxycinnamic acids (HCAs) and their esterified derivatives with their in vitro antifungal activity over Fusarium oxysporum f. sp. lycopersici. The antifungal activity of the tested HCAs, i.e., coumaric > ferulic > sinapinic > caffeic acid, was higher after esterification and when the coumaric acid hydroxyl group was at the ortho-position. This outcome was strengthened by the elongation of the alkyl chain to 4-carbons and, particularly, by the esterification with isobutyl alcohol. The highest antifungal activity was obtained from isobutyl o-coumarate (iBoC), which inhibits 70% of mycelial growth at 1.2 mM. Thereby, a heterogeneous catalysis strategy was optimized by using the response surface methodology. At the best conditions found, the synthesis of iBoC was scaled up to 15 g, achieving 96% conversion yield in 48 h in a stirred batch reactor. This study reveals for the first time the potential of iBoC to provide commercial materials as antifungal agents to control F. oxysporum and other phytopathogenic fungi.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03425-7.

Synthesis of homo- and copolymer containing sulfonic acid via atom transfer radical polymerization

Well-defined functional poly(p-phenyl styrenesulfonate) and poly(p-phenyl styrene-sulfonate-co-styrene) were successfully synthesized by the atom transfer radical polymerization (ATRP) using CuBr/bpy(PMDETA) catalyst and 1-phenylethyl bromide (1-PEBr) as an ATRP initiator in diphenyl ether (DPE) or dimethyl formamide (DMF). In both homo- and copolymers, the CuBr/PMDETA catalytic system in DPE or DME showed higher yield than CuBr/bpy and the polydispersity index (PDI) of polymer was low. Using PMDETA or bpy as a ligand in DMF, the high yield with high PDI was obtained than in DPE. We found that the CuBr/PMDETA catalyzed ATRP of p-phenyl styrenesulfonate and copolymerization with styrene comonomer in DPE proceeded in a controlled manner. The polymers containing sulfonic acid were obtained by the chemical deprotection of protecting group, followed by acidification. The molecular structure, molecular weights and thermal properties of the copolymers were determined by nuclear magnetic resonance (¹H NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively.

Cationic Polystyrene Resin Bound Silver Nanocomposites Assisted Fourier Transform Infrared Spectroscopy for Enhanced Catalytic Reduction of 4-Nitrophenol in Aqueous Medium

The present work reported a novel strategy to construct supported cationic-polystyrene-resin-bound silver nanocomposites for enhanced catalytic reduction of 4-nitrophenol in an aqueous medium. The Fourier transform infrared spectroscopy (FTIR) was used as a model instrument for the study of catalytic reduction of 4-nitrophenol using cationic-polystyrene-resin-bound silver nanocomposite materials. The mechanism is based on the reduction of 4-nitrophenol to 4-aminophenol due to the electron transfer process that occurred between donor borohydride (BH4−) and acceptor 4-nitrophenol. The polystyrene resin provides support and surface area to increase the catalytic activity of silver nanoparticles. The diffused reflectance-Fourier transform infrared spectroscopy revealed the binding of silver particles onto the surface of cationic polystyrene resin beads. Furthermore, the catalyst was easily separated by the filtration and drying process and was able to reuse. A quantitative analysis of this work has also been performed. The linearity range, the limit of detection, and the limit of quantification obtained for the present method were 0.1 × 10−4 to 1.0 M, 0.6 M, and 2.1 M, respectively. Moreover, a good catalytic efficiency was found to be 96.8%. The advantages of the current method are its simplicity, sensitivity, rapidity, low cost, ease of preparation, and excellent catalytic efficiency to reduce 4-nitrophenol from an aqueous solution.

Advances in Matrix-Supported Palladium Nanocatalysts for Water Treatment

Advanced catalysts are crucial for a wide range of chemical, pharmaceutical, energy, and environmental applications. They can reduce energy barriers and increase reaction rates for desirable transformations, making many critical large-scale processes feasible, eco-friendly, energy-efficient, and affordable. Advances in nanotechnology have ushered in a new era for heterogeneous catalysis. Nanoscale catalytic materials are known to surpass their conventional macro-sized counterparts in performance and precision, owing it to their ultra-high surface activities and unique size-dependent quantum properties. In water treatment, nanocatalysts can offer significant promise for novel and ecofriendly pollutant degradation technologies that can be tailored for customer-specific needs. In particular, nano-palladium catalysts have shown promise in degrading larger molecules, making them attractive for mitigating emerging contaminants. However, the applicability of nanomaterials, including nanocatalysts, in practical deployable and ecofriendly devices, is severely limited due to their easy proliferation into the service environment, which raises concerns of toxicity, material retrieval, reusability, and related cost and safety issues. To overcome this limitation, matrix-supported hybrid nanostructures, where nanocatalysts are integrated with other solids for stability and durability, can be employed. The interaction between the support and nanocatalysts becomes important in these materials and needs to be well investigated to better understand their physical, chemical, and catalytic behavior. This review paper presents an overview of recent studies on matrix-supported Pd-nanocatalysts and highlights some of the novel emerging concepts. The focus is on suitable approaches to integrate nanocatalysts in water treatment applications to mitigate emerging contaminants including halogenated molecules. The state-of-the-art supports for palladium nanocatalysts that can be deployed in water treatment systems are reviewed. In addition, research opportunities are emphasized to design robust, reusable, and ecofriendly nanocatalyst architecture.

Chirality-driven self-assembly: application toward renewable/exchangeable resin-immobilized catalysts

Resin-immobilized catalysts were prepared through chirality-driven self-assembly. The method allows the resin-immobilized catalyst to be regenerated under mild conditions and in situ catalyst exchange to be carried out quantitatively. The uniqueness of the methodology was demonstrated by the preparation of a catalyst for TEMPO oxidation as well as a two-step sequential TEMPO oxidation/aldol condensation sequence enabled by facile catalyst exchange.

Recent Advances in the Valorization of Biodiesel By-Product Glycerol to Solketal

The exponential rise of the biodiesel production has resulted in a considerable amount of glycerol as a by-product, which must be valorized to ensure the sector’s long-term viability. As a result, cost-effective glycerol conversions for significant value-added chemicals are essential for the biodiesel production in the long run. Solketal, a glycerol by-product, is obtained as a potential fuel additive in the biodiesel industry. Recently, several heterogeneous acid-catalysts stand out as a promising catalyst for solketal production where biomass-based catalyst gained attraction owing to their biodegradability, eco-friendly, and abundant availability. Furthermore, magnetic nanoparticles-derived catalysts along with sulfonated functionalized catalyzed, zeolites, resins, enzymatic, etc. have proved their efficiency in solketal production. In this review, a wider study on the recent advances of the catalysts has been discussed along with their preparation, various reaction parameters, its application, and efficiency for biodiesel industry. This study opens up incredible prospects for us to use renewable energy sources, which will benefit the industry, the environment, and the economy.

Fabrication and characterization of a toughened spherical chitosan adsorbent only through physical crosslinking based on mechanism of Chain Rearrangement

Chitosan extracted from natural products has gained tremendous attention in the field of adsorption and separation due to its inherent biocompatibility and potential applications. In this research, we synthesized a new type of spherical chitosan adsorbent (SCA) by controlling the mass transfer rate of the entanglement of the polymer chains in the recombination process. This SCA is a highly crystalline polymer material with outstanding mechanical strength, high adsorption capacity, a porous surface and suitable particle size distribution. The value of the sphericity of attrition of this SCA was 89.8%, which is the same as that of the commercial macroporous resin with a polystyrene matrix. The X-ray diffraction (XRD) patterns and differential scanning calorimetry (DSC) curves showed a significant change from powder to spherical structure and confirmed that the SCA is highly ordered and crystalline. Optical microscopy (OM) and scanning electron microscopy (SEM) demonstrated that the SCA was composed of a tightly stacked fiber structure, indicating the homogeneity of the polymerization. The porous structure of the surface provided a channel for mass transfer, which was indicated by a test of the ion exchange capacity and the adsorption performance of the SCA with Cu(ii) as the adsorbed subject. The adsorption capacity was higher than those of all reported non-composite chitosan materials. Therefore, we have successfully synthesized a completely green, nontoxic and environmentally friendly adsorbing resin equipped with excellent mechanical properties and adsorption capacity for future applications in many new fields.

Highly crystalline spherical chitosan ion exchange resins with numerous available functional groups and excellent mechanical performance can be produced on a large scale.

Cooperative catalysis of Cu/2,2,6,6-tetramethyl-1-piperidine-N-oxyl nanocatalysts supported by ultraviolet light-responsive polyimides

Azobenzene-containing polyimides were used as supports to immobilize pyrene-containing Cu/2,2,6,6-tetramethyl-1-piperidine-N-oxyl catalytic systems with UV-regulated cooperative behaviors.

Supramolecular Strategies for the Recycling of Homogeneous Catalysts

Supramolecular approaches are increasingly used in the development of homogeneous catalysts and they also provide interesting new tools for the recycling of metal-based catalysts. Various non-covalent interactions have been utilized for the immobilization homogeneous catalysts on soluble and insoluble support. By non-covalent anchoring the supported catalysts obtained can be recovered via (nano-) filtration or such catalytic materials can be used in continuous flow reactors. Specific benefits from the reversibility of catalyst immobilization by non-covalent interactions include the possibility to re-functionalize the support material and the use as "boomerang" type catalyst systems in which the catalyst is captured after a homogeneous reaction. In addition, new reactor design with implemented recycling strategies becomes possible, such as a reverse-flow adsorption reactor (RFA) that combines a homogeneous reactor with selective catalyst adsorption/desorpion. Next to these non-covalent immobilization strategies, supramolecular chemistry can also be used to generate the support, for example by generation of self-assembled gels with catalytic function. Although the stability is a challenging issue, some self-assembled gel materials have been successfully utilized as reusable heterogeneous catalysts. In addition, catalytically active coordination cages, which are frequently used to achieve specific activity or selectivity, can be bound to support by ionic interactions or can be prepared in structured solid materials. These new heterogenized cage materials also have been used successfully as recyclable catalysts.

Chemical micro-oscillators based on the Belousov–Zhabotinsky reaction

The results of studies on the development of micro-oscillators (MOs) based on the Belousov –Zhabotinsky (BZ) oscillatory chemical reaction are integrated and systematized. The mechanisms of the BZ reaction and the methods of immobilization of the catalyst of the BZ reaction in micro-volumes are briefly discussed. Methods for creating BZ MOs based on water microdroplets in the oil phase and organic and inorganic polymer microspheres are considered. Methods of control and management of the dynamics of BZ MO networks are described, including methods of MO synchronization. The prospects for the design of neural networks of MOs with intelligent-like behaviour are outlined. Such networks present a new area of nonlinear chemistry, including, in particular, the creation of a chemical ‘computer’.

The bibliography includes 250 references.

Characterization of polystyrene and polyacrylic based polymeric materials exposed to oxidative degradation

The characterization of oxidative degraded polystyrene-based resin (R1) and polyacrylic based resin (R2) resins in H2O2 and HClO4 degradation medium were made based on the kinetics and thermodynamic data obtained for the ion-isotopic exchange reactions using such resins. For the reactions performed by using resins degraded in H2O2 medium, the reaction rate (k) values obtained for the fresh R1 (0.315 min–1) and R2 (0.187 min–1) resins decreases to 0.300 and 0.155 min–1 respectively for the resins degraded in 20% H2O2 medium, which further decreases to 0.289 and 0.142 min–1 respectively for the resins degraded in 30% H2O2 medium. A similar trend in the results were observed for the reactions performed by using the above resins degraded in HClO4 medium. The higher values of k (min–1) and low values of various thermodynamic parameters for the ion-isotopic exchange reactions performed by using fresh and degraded polystyrene-based resin R1 resins suggests superior degradation stability as compared to polyacrylic based R2 resin.

Immobilization of an Iridium(I)-NHC-Phosphine Catalyst for Hydrogenation Reactions under Batch and Flow Conditions

Na2[Ir(cod)(emim)(mtppts)] (1) with high catalytic activity in various organic- and aqueous-phase hydrogenation reactions was immobilized on several types of commercially available ion-exchange supports. The resulting heterogeneous catalyst was investigated in batch reactions and in an H-Cube flow reactor in the hydrogenation of phenylacetylene, diphenylacetylene, 1-hexyne, and benzylideneacetone. Under proper conditions, the catalyst was highly selective in the hydrogenation of alkynes to alkenes, and demonstrated excellent selectivity in C=C over C=O hydrogenation; furthermore, it displayed remarkable stability. Activity of 1 in hydrogenation of levulinic acid to γ-valerolactone was also assessed.

Flexible reusable hierarchical hybrid catalyst for rapid and complete degradation of triclosan in water

A flexible, durable, and reusable nanocatalyst system was fabricated by anchoring palladium nanoparticles on carbon nanotube (CNT) carpets covalently attached to carbon cloth. These hierarchical hybrid materials were tested for catalytic degradation of triclosan (TCS), an emerging contaminant. Materials were characterized using scanning & transmission electron microscopy techniques (SEM and TEM), X-Ray Diffraction (XRD), and X-Ray Photoelectron Spectroscopy (XPS). The reaction kinetics was studied using HPLC and reaction pathways proposed based on LC-MS/GC-MS analyses. In the presence of hydrogen, complete step-wise chlorine removal was seen until complete dechlorination was accomplished. The pseudo-first-order rate constant was measured to be orders of magnitude higher than earlier reported values. Moreover, the same material was usable for multiple cycles in flowing water. This study demonstrates that robustness and reusability of larger structural materials can be combined with the ultra-high surface activity of nanocatalysts to provide practical and eco-friendly solutions for water sustainability.

A cost-effective combination of Rose Bengal and off-the-shelf cationic polystyrene for the photodynamic inactivation of Pseudomonas aeruginosa

Two new photoactive materials have been prepared, characterized and tested against Pseudomonas aeruginosa bacteria (planktonic suspension). The synthesis of the polymeric photosensitizers can be made at a multigram scale, in few minutes, starting from inexpensive and readily available materials, such as Rose Bengal (photosensitizer) and ion exchange resins Amberlite® IRA 900 (macroporous) or IRA 400 (gel-type) as cationic polystyrene supports. The most notable feature of these systems is their notable bactericidal activity in the dark (4-5 log₁₀ CFU/mL reduction of the population of P. aeruginosa) which becomes enhanced upon irradiation with visible light (to reach a total reduction of 8 log₁₀ CFU/mL for the macroporous polymer at a fluence of 120 J/cm² using green light of 515 nm).

Synthesis of quinazoin-4-ones through an acid ion exchange resin mediated cascade reaction

An interesting cascade reaction of N-(2-(4,5-dihydrooxazol-2-yl)phenyl)benzamide in the presence of an acid ion exchange resin is described. In this reaction, a range of substrates bearing various substituent groups are well compatible. This work provides a green and atom-economical alternative approach for the synthesis of quinazolin-4-ones in good yields.

Heterogeneous catalysis for the tandem cyclisation of unsaturated alcohols

A methodology for the tandem cycloisomerisation of doubly unsaturated alcohols using Amberlyst-15 was developed.

Anion exchange behavior of MIIAl layered double hydroxides: a molecular dynamics and DFT study

The ion exchange reaction has been extensively used in the field of synthesis of functionalized supramolecular materials such as layered double hydroxides (LDHs), ion-embedded batteries, sewage disposal and so on. In this work, the factors influencing the anion exchange behavior in the LDH gallery, such as the exchange domain, the exchange order, the driving force, and the diffusion of the anions, are investigated systematically using molecular dynamics (MD) simulations and density functional theory (DFT) methods in view of both thermodynamics and dynamics. 159 models of MIIRAl-A-LDHs (MII = Mg, Ni, Zn; R = 1.4-8, A = OH-, Cl-, Br-, NO3-, HCOO-, C6H5SO3-, CO32-, SO42-, and PO43-, respectively) are calculated. The results reveal that the anion exchange domain (interlayer distance) in LDHs is determined not only by the size and their arrangement modes of the guest anions, but also by the charges the anions carry. The relative binding energies of different anions and the Gibbs free energy changes of the anion exchange reactions in LDHs decrease in the order of PO43- > CO32- > SO42- > OH- > Cl- > Br- > HCOO- > NO3- > C6H5SO3-, which is in accordance with the experimental anion exchange order. The stronger the hydrogen bonding between the anion and the host, the larger the charge transfer, and the smaller the electronegativity of the anion, the more difficult it is for the anion to be exchanged out from LDH interlayer. In addition, for the anions with the same charges, the relative binding energy is linearly well correlated with the interlayer spacing. By analyzing the contribution of each energetic item comprising the total potential energy, it is found that the major driving force of anion exchange is the electrostatic force. The diffusion coefficient (D) along the c direction is nearly equal to zero, suggesting that the diffusion of anions occurs mainly in the ab plane of the LDH cell. It also can be inferred that when the cell parameter c < 24.0 Å, the anion exchange order is mainly determined by the thermodynamic factors, whereas when c > 24.0 Å, both the thermodynamic and the dynamic factors cast the same effect on the anion exchange behavior. This work provides an in-depth understanding of the anion exchange behavior, and is helpful guidance for the design and synthesis of functionalized guest anion intercalated LDHs and related materials using the anion-exchange method.

Recent advances in catalytic asymmetric dihydroxylation of olefins

Asymmetric dihydroxylation of olefinic groups is an extremely important synthetic transformation which has been widely utilized to obtain optically pure pharmaceuticals and other fine chemical products. In recent years, catalyst systems for the asymmetric C=C dihydroxylations have attracted significant interest, the major research efforts being focused on designing environmentally benign catalyst systems. This mini-review summarizes recent progress in the field, surveying both novel, less toxic modifications of the classical osmium-based catalysts, and the highly efficient and enantioselective non-osmium catalyst systems.

The bibliography includes 50 references.

New Approach for the One-Pot Synthesis of 1,3,5-Triazine Derivatives: Application of Cu(I) Supported on a Weakly Acidic Cation-Exchanger Resin in a Comparative Study

An efficient and simple methodology for Ullmann Cu(I)-catalyzed synthesis of di- and trisubstituted 1,3,5-triazine derivatives from dichlorotriazinyl benzenesulfonamide and corresponding nucleophiles is reported. Cations Cu(I) supported on macroporous and weakly acidic, low-cost industrial resin of polyacrylate type were used as a catalyst. The reaction times and yields were compared with traditional synthetic methods for synthesis of substituted 1,3,5-triazine derivatives via nucleophilic substitution of chlorine atoms in dichlorotriazinyl benzenesulfonamide. It was found that Ullmann-type reactions provide significantly shortened reaction times and, in some cases, also higher yields. Finally, trisubstituted s-triazine derivatives were effectively prepared via Ullmann-type reaction in a one-pot synthetic design. Six new s-triazine derivatives with potential biological activity were prepared and characterized.

Preparation and Study of Reusable Polymerized Catalysts for Ester Hydrogenation

A cross-linked catalyst organic framework was prepared by an alternating ring-opening olefin metathesis polymerization between dichloro{N,N'-bis({(2-diphenylphosphino)phenyl}methylidene)bicyclo[2.2.1]-hept-5-ene-2,3-diamine}ruthenium, 1,2-N-di(cis-5-norbornene-2,3-endo-dicarboximido)-ethane, and cis-cyclooctene catalyzed by RuCl2(=CHPh)(PCy3)2 in the presence of a BaSO4 support. The heterogenized catalyst hydrogenated methyl benzoate at a similar rate to the homogeneous catalyst (0.0025 mol % catalyst, 10 mol % KO t Bu, 80 °C, 50 atm, tetrahydrofuran, 21 h, ∼15 000 turnovers during the first 1 h). The catalyst was used five times for a total of 121 680 turnovers. A study on the reusability of this catalyst showed that ester hydrogenations with bifunctional catalysts slow as the reaction proceeds. This inhibition is removed by isolating and reusing the catalyst, suggesting that future catalyst design should emphasize avoiding product inhibition.

Continuous-Flow Oxidation of HMF to FDCA by Resin-Supported Platinum Catalysts in Neat Water

The oxidation reaction of 5-hydroxymethylfurfural to the bioplastic monomer 2,5-furandicarboxylic acid over heterogenous resin-supported Pt catalysts was investigated in detail, under continuous flow, base-free conditions, and in neat water. The product was continuously obtained in 99 % yield by running the reaction at 120 °C, 303 s residence time, 1.2 mL min^-1 O₂ flow rate, and 7.7 bar O₂ pressure. The product was isolated with a high space-time-yield of 46.0 g L^-1  h^-1 without purifications or acid/base treatments.

Developing two-dimensional solid superacids with enhanced mass transport, extremely high acid strength and superior catalytic performance

Solid acids have been widely used as heterogeneous catalysts in developing green and sustainable chemistry. However, it remains a challenge to improve the mass transport properties and acid strength of solid acids simultaneously. Herein, we report a class of two dimensional (2D) layered hybrid solid acids with outstanding mass transfer and extremely high acid strength by incorporating sulfonated polymers in-between montmorillonite layers. The 2D layered structure and broad distribution of pore sizes allow for highly efficient mass transport of substrate molecules into and out of the solid acids. The acid strength of these solid acids was found to be stronger than that of 100% H₂SO₄, H₃PW₁₂O₄₀ and any other reported solid acids to date, as determined by ¹H and ³¹P solid-state NMR. These 2D solid acids show extraordinary catalytic performance in biomass conversion to fuels, superior to that of H₃PW₁₂O₄₀, HCl and H₂SO₄. Theoretical calculations and control experiments reveal that H-bond based interactions between the polymer and montmorillonite facilitate the unusually high acid strengths found in these samples.

Recent Advances Utilized in the Recycling of Homogeneous Catalysis

Homogeneous catalysts often show high activity and selectivity towards the various chemical transformations. Most of the transition metal-based active catalysts are expensive, rare, and have strict regulations for their use in pharmaceutical products. Hence, there is a requirement to develop suitable technologies for the practical separation and recycling of metal complex catalysts along with the sustainability of the process. This review focuses on the recent techniques used for the catalyst separation, their recovery, and recyclability of the homogeneous form of catalysts based on their economic compatibility and industrial applications. Various homogeneous catalysts have been reviewed on the basis of their support or media, active centres and recyclability aspects of the catalysts. This review gives brief insights into the varied examples of different recycling techniques utilized in the past 6-7 years.

Hierarchical nanomaterials via biomolecular self-assembly and bioinspiration for energy and environmental applications

Bioinspired synthesis offers potential green strategies to build highly complex nanomaterials by utilizing the unique nanostructures, functions, and properties of biomolecules, in which the biomolecular recognition and self-assembly processes play important roles in tailoring the structures and functions of bioinspired materials. Further understanding of biomolecular self-assembly for inspiring the formation and assembly of nanoparticles would promote the design and fabrication of functional nanomaterials for various applications. In this review, we focus on recent advances in bioinspired synthesis and applications of hierarchical nanomaterials based on biomolecular self-assembly. We first discuss biomolecular self-assembly towards biological nanomaterials, in which the mechanisms and ways of biomolecular self-assembly as well as various self-assembled biomolecular nanostructures are demonstrated. Secondly, the bioinspired synthesis strategies including molecule-molecule interaction, molecule-material recognition, molecule-mediated nucleation and growth, and molecule-mediated reduction/oxidation are introduced and discussed. Meanwhile, typical examples and discussions on how biomolecular self-assembly inspires the formation of hierarchical hybrid nanomaterials are presented. Finally, the applications of bioinspired nanomaterials in biofuel cells, light-harvesting systems, batteries, supercapacitors, catalysis, water/air purification, and environmental monitoring are presented and discussed. We believe that this review will be very helpful for readers to understand the self-assembly of biomolecules and the biomimetic/bioinspired strategies for synthesizing hierarchical nanomaterials on the one hand, and on the other hand to design novel materials for extended applications in nanotechnology, materials science, analytical science, and biomedical engineering.

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.

Quantitative Evaluation of the Effect of the Hydrophobicity of the Environment Surrounding Brønsted Acid Sites on Their Catalytic Activity for the Hydrolysis of Organic Molecules

Sulfo-functionalized siloxane gels with a variety of surface hydrophobicities were fabricated to elucidate the effect of the environment surrounding the Brønsted acid site on their catalytic activity for the hydrolysis of organic molecules. A detailed structural analysis of these siloxane gels by elemental analysis, X-ray photoelectron spectroscopy, Fourier-transformed infrared (FT-IR), and ²⁹Si MAS NMR revealed the formation of gel catalysts with a highly condensed siloxane network, which enabled us to quantitatively evaluate the hydrophobicity of the environment surrounding the catalytically active sulfo-functionality. A sulfo group in a highly hydrophobic environment exhibited excellent catalytic turnover frequency for the hydrolysis of acetate esters with a long alkyl chain, whereas not only conventional solid acid catalysts but also liquid acids showed quite low catalytic activity. Detailed kinetic studies corroborated that the adsorption of oleophilic esters at the Brønsted acid site was facilitated by the surrounding hydrophobic environment, thus significantly promoting hydrolysis under aqueous conditions. Furthermore, sulfo-functionalized siloxane gels with a highly hydrophobic surface showed excellent catalytic activity for the hydrolytic deprotection of silyl ethers.

Polymer immobilized tantalum(v)–amino acid complexes as selective and recyclable heterogeneous catalysts for oxidation of olefins and sulfides with aqueous H2O2

Polymer supported peroxotantalate based heterogeneous catalysts served as highly efficient, selective and recyclable catalysts for alkene epoxidation and sulfide oxidation with green oxidant aqueous H₂O₂ under mild reaction conditions.