Fabrication of Ruthenium Nanoparticles in Porous Organic Polymers: Towards Advanced Heterogeneous Catalytic Nanoreactors

Palladium-anchored calix[4]arene-derived porous organic polymer towards efficient hydrolytic cleavage of carbon disulfide

The release of carbon disulfide can have adverse effects on our environment and human health. The stability of carbon disulfide and the slow kinetics of hydrolysis can make it challenging to achieve efficient and practical cleavage of the CS bonds. Herein, a calix[4]arene-based porous organic polymer (CPOP-1) is innovatively synthesized through an optimized polycondensation reaction using C-Methylcalix[4]resorcinarene and hexafluoro-hexaazatriphenylene as monomers. Subsequently, palladium-induced calix[4]arene-based porous organic polymer was also synthesized via strong Pd-N coordination bonds to construct the metal-induced porous catalyst (CPOP-2). The polymeric catalyst active center [Pd2+(N^N)(NO3-)2] demonstrated outstanding catalytic hydrolysis performance (11.14 μmol g-1 h-1) in 10.5 h which is significantly enhanced by ca.13.2 times as compared to reported mononuclear Bpy-Pd(NO3)2, and 7.07 times than model trinuclear complex catalyst HATN-Pd-1, respectively. The control experiments revealed that POP catalysts showcased robust stability, prolonged effectiveness, and feasible recyclability during the hydrolytic cleavage of carbon disulfide at room temperature in aqueous solutions. Furthermore, the coordination environment of [Pd2+(N^N)] was validated through XPS, EXAFS, and isotope labeling measurements, and the hydrolysis cleavage products were confirmed e. g. CO2, sulfide, and protons. More importantly, a reaction mechanism was formulated coupled with theoretical calculations, and simulations. The proposed mechanism involves sequential OH- nucleophilic attacks on the carbon atoms of insert-coordinated CS2 and COS, leading to the cleavage of double CS bonds and the formation of CO bonds. The concurrent dissociation of the C-S bond and liberation of CO2 result in an intermediate structure characterized by [(N^N)Pd2+](SH-)2. This intermediate motif serves as the source of the thermodynamic driving force for the reaction.

Hydrogenation of levulinic acid to γ-valerolactone over hydrophobic Ru@HCP catalysts

This study introduces an efficient strategy for promoting the synthesis of γ-valerolactone (GVL) via levulinic acid (LA) hydrogenation. A series of hyper-crosslinked porous polymer (HCP) supported Ru catalysts with different monomers were prepared. The wettabilities were controlled by the surface functional groups. The hydrophobic catalysts showed much higher activity than the hydrophilic ones in the hydrogenation of LA to GVL, highly possible due to the substrate enrichment. Further insight showed that the reaction proceeded through the 4-HVA route. These results illustrated the importance of surface wettability in bio-based molecule upgrading, which is beneficial for catalyst design.

Fabrication, Facilitating Gas Permeability, and Molecular Simulations of Porous Hypercrosslinked Polymers Embedding 6FDA-Based Polyimide Mixed-Matrix Membranes

Novel polymers applied in economic membrane technologies are a perennial hot topic in the fields of natural gas purification and O₂ enrichment. Herein, novel hypercrosslinked polymers (HCPs) incorporating 6FDA-based polyimide (PI) MMMs were prepared via a casting method for enhancing transport of different gases (CO₂, CH₄, O₂, and N₂). Intact HCPs/PI MMMs could be obtained due to good compatibility between the HCPs and PI. Pure gas permeation experiments showed that compared with pure PI film, the addition of HCPs effectively promotes gas transport, increases gas permeability, and maintains ideal selectivity. The permeabilities of HCPs/PI MMMs toward CO₂ and O₂ were as high as 105.85 Barrer and 24.03 Barrer, respectively, and the ideal selectivities of CO₂/CH₄ and O₂/N₂ were 15.67 and 3.00, respectively. Molecular simulations further verified that adding HCPs was beneficial to gas transport. Thus, HCPs have potential utility in fabrication of MMMs for facilitating gas transport in the fields of natural gas purification and O₂ enrichment.

Hyper crosslinked polymer supported NHC stabilized gold nanoparticles with excellent catalytic performance in flow processes

Highly active and selective heterogeneous catalysis driven by metallic nanoparticles relies on a high degree of stabilization of such nanomaterials facilitated by strong surface ligands or deposition on solid supports. In order to tackle these challenges, N-heterocyclic carbene stabilized gold nanoparticles (NHC@AuNPs) emerged as promising heterogeneous catalysts. Despite the high degree of stabilization obtained by NHCs as surface ligands, NHC@AuNPs still need to be loaded on support structures to obtain easily recyclable and reliable heterogeneous catalysts. Therefore, the combination of properties obtained by NHCs and support structures as NHC bearing "functional supports" for the stabilization of AuNPs is desirable. Here, we report the synthesis of hyper-crosslinked polymers containing benzimidazolium as NHC precursors to stabilize AuNPs. Following the successful synthesis of hyper-crosslinked polymers (HCP), a two-step procedure was developed to obtain HCP·NHC@AuNPs. Detailed characterization not only revealed the successful NHC formation but also proved that the NHC functions as a stabilizer to the AuNPs in the porous polymer network. Finally, HCP·NHC@AuNPs were evaluated in the catalytic decomposition of 4-nitrophenol. In batch reactions, a conversion of greater than 99% could be achieved in as little as 90 s. To further evaluate the catalytic capability of HCP·NHC@AuNP, the catalytic decomposition of 4-nitrophenol was also performed in a flow setup. Here the catalyst not only showed excellent catalytic conversion but also exceptional recyclability while maintaining the catalytic performance.

Ultrasound-assisted green synthesis of Ru supported on LDH-CNT composites as an efficient catalyst for N-ethylcarbazole hydrogenation

N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NEC/12H-NEC) is one of the most attractive LOHCs, and it is of great significance to develop catalysts with high activity and reduce the hydrogen storage temperature. Layered double hydroxides-carbon nanotubes composites (LDH-CNT) were synthesized by a simple in-situ assembly method. Due to the introduction of CNT, a strong interaction occurred between LDH and CNT, which effectively improved the electron transfer ability of LDH-CNT. Ru/LDH-CNT catalysts were prepared via ultrasound-assisted reduction method without adding reducing agents and stabilizers. Under the cavitation effect of ultrasound, the hydroxyl groups on the surface of LDH were excited to generate hydrogen radicals (•H) with high reducibility, which successfully reduced Ru3+ to Ru NPs. Ru/LDH-3.9CNT-(300-1) catalyst was of 1.63 nm average Ru particle size with CNT amount of 3.9 wt% and the ultrasonic power of 300 W at 1 h, and its electron transfer resistance was less than that of Ru/LDH-(300-1). The synergy of ultrafine Ru NPs and fast electron transfer made it exhibit exceptional catalytic performance in NEC hydrogenation. Even if the reaction temperature was lowered to 80 °C, its hydrogenation performance was better than that of commercial Ru/Al2O3 catalyst at 120 °C. The ultrasound-assisted method is efficient, green and environmentally friendly, and the operation process is simple and economical. It is expected to be used in practical industrial production, which provides a reference for the preparation of high-activity and low-temperature hydrogen storage catalysts.

Construction of a (NNN)Ru-Incorporated Porous Organic Polymer with High Catalytic Activity for β-Alkylation of Secondary Alcohols with Primary Alcohols

Solid supports functionalized with molecular metal catalysts combine many of the advantages of heterogeneous and homogeneous catalysis. A (NNN)Ru-incorporated porous organic polymer (POP-bp/bbpRuCl₃) exhibited high catalytic efficiency and broad functional group tolerance in the C–C cross-coupling of secondary and primary alcohols to give β-alkylated secondary alcohols. This catalyst demonstrated excellent durability during successive recycling without leaching of Ru which is ascribed to the strong binding of the pincer ligands to the metal ions.

Highly efficient and selective aqueous phase hydrogenation of aryl ketones, aldehydes, furfural and levulinic acid and its ethyl ester catalyzed by phosphine oxide-decorated polymer immobilized ionic liquid-stabilized ruthenium nanoparticles

Phosphine oxide-decorated polymer immobilized ionic liquid stabilized RuNPs catalyse the hydrogenation of aryl ketones with remarkable selectivity for the CO bond, complete hydrogenation to the cyclohexylalcohol and hydrogenation of levulinic acid to γ-valerolactone.

Mechanism of Producing Metallic Nanoparticles, with an Emphasis on Silver and Gold Nanoparticles, Using Bottom-Up Methods

Bottom-up nanoparticle (NP) formation is assumed to begin with the reduction of the precursor metallic ions to form zero-valent atoms. Studies in which this assumption was made are reviewed. The standard reduction potential for the formation of aqueous metallic atoms-E0(Mn+aq/M0aq)-is significantly lower than the usual standard reduction potential for reducing metallic ions Mn+ in aqueous solution to a metal in solid state. E0(Mn+aq/M0solid). E0(Mn+aq/M0aq) values are negative for many typical metals, including Ag and Au, for which E0(Mn+aq/M0solid) is positive. Therefore, many common moderate reduction agents that do not have significantly high negative reduction standard potentials (e.g., hydrogen, carbon monoxide, citrate, hydroxylamine, formaldehyde, ascorbate, squartic acid, and BH4-), and cannot reduce the metallic cations to zero-valent atoms, indicating that the mechanism of NP production should be reconsidered. Both AgNP and AuNP formations were found to be multi-step processes that begin with the formation of clusters constructed from a skeleton of M+-M+ (M = Ag or Au) bonds that is followed by the reduction of a cation M+ in the cluster to M0, to form Mn0 via the formation of NPs. The plausibility of M+-M+ formation is reviewed. Studies that suggest a revised mechanism for the formation of AgNPs and AuNPs are also reviewed.

On the Differences in the Mechanisms of Reduction of AuCl2- and Ag(H2O)2+ with BH4. J Phys Chem A 2020;124:10765-10776. [PMID: 33319563 DOI: 10.1021/acs.jpca.0c06610]

The mechanism of reduction of AuCl₄^-/AuCl₃OH^- by BH₄^- was analyzed by density functional theory (DFT). The results point out that Au_atoms⁰ are not intermediates in the process. The derived mechanism differs considerably from that reported for the analogous process involving the reduction of Ag(H₂O)₂⁺ by BH₄^-. Thus, though both processes follow the Creighton procedure, the detailed mechanism differs significantly. For Au, the agglomeration starts with AuH₂^-, whereas for Ag, it starts with (H₂O)AgH. Stopped-flow measurements support the complicated mechanism.

Design of Organic/Inorganic Hybrid Catalysts for Energy and Environmental Applications

Controlling selectivity between competing reaction pathways is crucial in catalysis. Several approaches have been proposed to achieve this goal in traditional heterogeneous catalysts including tuning nanoparticle size, varying alloy composition, and controlling supporting material. A less explored and promising research area to control reaction selectivity is via the use of hybrid organic/inorganic catalysts. These materials contain inorganic components which serve as sites for chemical reactions and organic components which either provide diffusional control or directly participate in the formation of active site motifs. Despite the appealing potential of these hybrid materials to increase reaction selectivity, there are significant challenges to the rational design of such hybrid nanostructures. Structural and mechanistic characterization of these materials play a key role in understanding and, therefore, designing these organic/inorganic hybrid catalysts. This Outlook highlights the design of hybrid organic/inorganic catalysts with a brief overview of four different classes of materials and discusses the practical catalytic properties and opportunities emerging from such designs in the area of energy and environmental transformations. Key structural and mechanistic characterization studies are identified to provide fundamental insight into the atomic structure and catalytic behavior of hybrid organic/inorganic catalysts. Exemplary works are used to show how specific active site motifs allow for remarkable changes in the reaction selectivity. Finally, to demonstrate the potential of hybrid catalyst materials, we suggest a characterization-based approach toward the design of biomimetic hybrid organic/inorganic materials for a specific application in the energy and environmental research space: the conversion of methane into methanol.

A magnetically separable and recyclable g-C3N4/Fe3O4/porous ruthenium nanocatalyst for the photocatalytic degradation of water-soluble aromatic amines and azo dyes

Herein, we present the development of a visible-light-driven magnetically retrievable nanophotocatalyst made of porous ruthenium nanoparticles supported on magnetic carbon nitride (g-C3N4/Fe3O4/p-RuNP) for the facile removal/degradation of aromatic amines and azo dyes from wastewater. Aromatic amines and azo-based dyes in water bodies are highly toxic and carcinogenic even at very low concentrations and are difficult to separate because of their high solubility. Our nanocatalyst can efficiently degrade/decompose the aromatic amines and azo dyes under visible light (LED/sunlight) at room temperature and in a wide pH range (pH 5.0-9.0) without using any external chemicals. The magnetic property of the nanocatalyst facilitates its efficient and facile separation from the reaction mixture for reuse in multiple photocatalytic cycles. The nanocatalyst-based degradation of azo dyes and aromatic amines presented here is simple and convenient in terms of efficiency, energy, reusability and cost. The process also does not require any external chemicals and forms gaseous/less harmful end products.

On the mechanism of reduction of M(H2O)mn+ by borohydride: the case of Ag(H2O)2. NANOSCALE 2020;12:1657-1672. [PMID: 31894221 DOI: 10.1039/c9nr08472j]

The redox potentials of M(H2O)mn+/M0(atom) couples are often far too negative to enable the formation of M0(atom) by most reducing agents. Therefore, one has to reconsider the mechanism of formation of M0-NPs by the bottom-up procedure. A deep and detailed theoretical analysis of the reduction of Ag(H2O)2+ by BH4- points out that silver cations act mainly as catalysts of the reactions BH4- + 4H2O → B(OH)4- + 4H2. However, the transition states of the catalyzed process differ from those of the un-catalyzed process. The formation of (H2O)Ag-H, which is the starting stage for the formation of intermediates with Ag-Ag bonds, is only a side reaction in the process. Experimental evidence of the complexity of the process is presented, by stopped-flow; at least four processes are observed prior to the formation of Ag0-NPs. The spectra of these intermediates differ from those of Ag0atom and Ag2+aq. Though DFT calculations were performed only for silver cations, it is believed that analogous mechanisms are involved in the reductions of other cations.

Rapid Polymerization of Aromatic Vinyl Monomers to Porous Organic Polymers via Acid Catalysis at Mild Condition

Porous organic polymers (POPs) have enormous applications in various fields and thus have received a lot of research attention in recent decades. Numerous synthetic methods have been developed, but mild synthesis conditions and fast polymerization rate are highly desired. Herein, high porous POPs with high surface areas from aromatic vinyl monomers by using acid catalysis method is reported. The polymerization is ultrafast and could be accomplished even in 5 min at room temperature. Furthermore, the surface area can be tuned by using various acid catalysts and controlling the reaction time. Due to the high surface area, these POPs show promising adsorption of carbon dioxide and hydrogen, respectively. Furthermore, the large π-system of the building block and high surface area of the POPs also make them show potential applications in photocatalytic hydrogen evolution as well as promising catalyst support for metal nanoparticles.

On the Gas Storage Properties of 3D Porous Carbons Derived from Hyper-Crosslinked Polymers

The preparation of porous carbons by post-synthesis treatment of hypercrosslinked polymers is described, with a careful physico-chemical characterization, to obtain new materials for gas storage and separation. Different procedures, based on chemical and thermal activations, are considered; they include thermal treatment at 380 °C, and chemical activation with KOH followed by thermal treatment at 750 or 800 °C; the resulting materials are carefully characterized in their structural and textural properties. The thermal treatment at temperature below decomposition (380 °C) maintains the polymer structure, removing the side-products of the polymerization entrapped in the pores and improving the textural properties. On the other hand, the carbonization leads to a different material, enhancing both surface area and total pore volume—the textural properties of the final porous carbons are affected by the activation procedure and by the starting polymer. Different chemical activation methods and temperatures lead to different carbons with BET surface area ranging between 2318 and 2975 m²/g and pore volume up to 1.30 cc/g. The wise choice of the carbonization treatment allows the final textural properties to be finely tuned by increasing either the narrow pore fraction or the micro- and mesoporous volume. High pressure gas adsorption measurements of methane, hydrogen, and carbon dioxide of the most promising material are investigated, and the storage capacity for methane is measured and discussed.

Robust ultrafine ruthenium nanoparticles enabled by covalent organic gel precursor for selective reduction of nitrobenzene in water

Metal nanoparticles (NPs) supported on nitrogen-doped porous carbon (NPC) are one type of promising heterogeneous catalysts. The tuning and understanding of metal-support interactions are crucial for the design and synthesis of highly durable and efficient heterogeneous catalytic systems. Here, we present an effective strategy to integrate ultrafine metal NPs into NPC via utilizing a covalent organic gel (COG) as the precursor for the first time. The ruthenium (Ru) NPs were uniformly dispersed in NPCs with the average size as low as 1.90 ± 0.4 nm. Irrespective of their ultrafine size, Ru NPs showed unprecedented stability and recyclability in Ru-catalyzed reduction of nitrobenzene and were greatly superior to commercial Ru/C and NPC-supported Ru NPs synthesized by the traditional post-loading method. This synthetic strategy can be extended to the synthesis of other metal or alloy NPs for a variety of advanced applications.

The Chemical Properties of Hydrogen Atoms Adsorbed on M0 -Nanoparticles Suspended in Aqueous Solutions: The Case of Ag0 -NPs and Au0 -NPs Reduced by BD4. Angew Chem Int Ed Engl 2018;57:16525-16528. [PMID: 30320944 DOI: 10.1002/anie.201809302]

The nature of H-atoms adsorbed on M⁰ -nanoparticles is of major importance in many catalyzed reduction processes. Using isotope labeling, we determined that hydrogen evolution from transient {(M⁰ -NP)-H_n }^n- proceeds mainly via the Heyrovsky mechanism when n is large (i.e., the hydrogens behave as hydrides) but mainly via the Tafel mechanism when n is small (i.e., the hydrogens behave as atoms). Additionally, the relative contributions of the two mechanisms differ considerably for M=Au and Ag. The results are analogous to those recently reported for the M⁰ -NP-catalyzed de-halogenation processes.

Simple Preparation of Porous Carbon-Supported Ruthenium: Propitious Catalytic Activity in the Reduction of Ferrocyanate(III) and a Cationic Dye

The present study involves the synthesis, characterization, and catalytic application of ruthenium nanoparticles (Ru NPs) supported on plastic-derived carbons (PDCs) synthesized from plastic wastes (soft drink bottles) as an alternative carbon source. PDCs have been further activated with CO₂ and characterized by various analytical techniques. The catalytic activity of Ru@PDC for the reduction of potassium hexacyanoferrate(III), (K₃[Fe(CN)₆]), and new fuchsin (NF) dye by NaBH₄ was performed under mild conditions. The PDCs had spherical morphology with an average size of 0.5 μm, and the Ru NP (5 ± 0.2 nm) loading (4.01 wt %) into the PDC provided high catalytic performance for catalytic reduction of ferrocyanate(III) and NF dye. This catalyst can be recycled more than six times with only a minor loss of its catalytic activity. In addition, the stability and reusability of the Ru@PDC catalyst are also discussed.

Advances in Nanostructured Metal-Encapsulated Porous Organic-Polymer Composites for Catalyzed Organic Chemical Synthesis

Porous organic polymers (POPs) are of growing research interest owing to their high surface areas, stabilities, controllable chemical configurations, and tunable pore volumes. The molecular nanoarchitecture of POP provides metal or metal oxide binding sites, which is promising for the development of advanced heterogeneous catalysts. This article highlights the development of numerous kinds of POPs and key achievements to date, including their functionalization and incorporation of nanoparticles into their framework structures, characterization methods that are predominantly in use for POP-based materials, and their applications as catalysts in several reactions. Scientists today are capable of preparing POP-based materials that show good selectivity, activity, durability, and recoverability, which can help overcome many of the current environmental and industrial problems. These POP-based materials exhibit enhanced catalytic activities for diverse reactions, including coupling, hydrogenation, and acid catalysis.

Feasibility Study on the Design and Synthesis of Functional Porous Organic Polymers with Tunable Pore Structure as Metallocene Catalyst Supports

Porous organic polymers (POPs) are highly versatile materials that find applications in adsorption, separation, and catalysis. Herein, a feasibility study on the design and synthesis of POP supports with a tunable pore structure and high ethylene-polymerization activity was conducted by the selection of functional comonomers and template agents, and control of cross-linking degree of their frameworks. Functionalized POPs with a tunable pore structure were designed and synthesized by a dispersion polymerization strategy. The functional comonomers incorporated in the poly(divinylbenzene) (PDVB)-based matrix played a significant role in the porous structure and particle morphology of the prepared polymers, and a specific surface area (SSA) of 10–450 m²/g, pore volume (PV) of 0.05–0.5 cm³/g, bulk density with a range of 0.02–0.40 g/cm³ were obtained by the varied functional comonomers. Besides the important factors of thermodynamic compatibility of the selected solvent system, other factors that could be used to tune the pore structure and morphology of the POP particles have been also investigated. The Fe₃O₄ nanoaggregates as a template agent could help improve the porous structure and bulk density of the prepared POPs, and the highly cross-linking networks can dramatically increase the porous fabric of the prepared POPs. As for the immobilized metallocene catalysts, the pore structure of the prepared POPs had a significant influence on the loading amount of the Zr and Al of the active sites, and the typically highly porous structure of the POPs would contribute the immobilization of the active species. High ethylene-polymerization activity of 8033 kg PE/mol Zr h bar was achieved on the POPs-supported catalysts, especially when high Al/Zr ratios on the catalysts were obtained. The performance of the immobilized metallocene catalysts was highly related to the pore structure and functional group on the POP frameworks.

Hypercrosslinked porous polymer materials: design, synthesis, and applications

Hypercrosslinked polymers (HCPs) are a series of permanent microporous polymer materials initially reported by Davankov, and have received an increasing level of research interest. In recent years, HCPs have experienced rapid growth due to their remarkable advantages such as diverse synthetic methods, easy functionalization, high surface area, low cost reagents and mild operating conditions. Judicious selection of monomers, appropriate length crosslinkers and optimized reaction conditions yielded a well-developed polymer framework with an adjusted porous topology. Post fabrication of the as developed network facilitates the incorporation of various chemical functionalities that may lead to interesting properties and enhance the selection toward a specific application. To date, numerous HCPs have been prepared by post-crosslinking polystyrene-based precursors, one-step self-polycondensation or external crosslinking strategies. The advent of these methodologies has prompted researchers to construct well-defined porous polymer networks with customized micromorphology and functionalities. In this review, we describe not only the basic synthetic principles and strategies of HCPs, but also the advancements in the structural and morphological study as well as the frontiers of potential applications in energy and environmental fields such as gas storage, carbon capture, removal of pollutants, molecular separation, catalysis, drug delivery, sensing etc.

Cu–Pd bimetallic nanoalloy anchored on a N-rich porous organic polymer for high-performance hydrodeoxygenation of biomass-derived vanillin

A N-rich porous organic polymer-anchored bimetallic Cu–Pd nanoalloy exhibited superior catalytic activity with improved stability for biomass-derived selective hydrodeoxygenation of vanillin.

Preparation of multifunctional hollow microporous organic nanospheres via a one-pot hyper-cross-linking mediated self-assembly strategy

Multifunctional hollow microporous organic nanospheres (HMONs) were successfully synthesized via a one-pot hyper-cross-linking mediated self-assembly strategy.

Chloromethylated polystyrene immobilized ruthenium complex of 2-(2-pyridyl)benzimidazole catalyst for the synthesis of bioactive disubstituted ureas by carbonylation reaction

Recyclable Ru–Py–Merf catalyst is synthesized and well characterized. The catalytic study of Ru–Py–Merf was performed for the synthesis of disubstituted ureas with high yield.

A new strongly paramagnetic cerium-containing microporous MOF for CO2 fixation under ambient conditions

A new microporous Ce₂NDC₃ MOF has been synthesized solvothermally and it displayed strong paramagnetism and high catalytic efficiency in CO₂ fixation under ambient conditions for the synthesis of cyclic carbonates.

Hydroxy-functionalized hyper-cross-linked ultra-microporous organic polymers for selective CO2 capture at room temperature

Two hydroxy-functionalized hyper-cross-linked ultra-microporous compounds have been synthesized by Friedel–Crafts alkylation reaction and characterised with different spectroscopic techniques. Both compounds exhibit an efficient carbon dioxide uptake over other gases like N₂, H₂ and O₂ at room temperature. A high isosteric heat of adsorption (Q_st) has been obtained for both materials because of strong interactions between polar –OH groups and CO₂ molecules.