Pd Nanoparticles Decorated on Hypercrosslinked Microporous Polymer: A Highly Efficient Catalyst for the Formylation of Amines through Carbon Dioxide Fixation

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.

Borohydride Ionic Liquids as Reductants of CO2 in the Selective N-formylation of Amines

Borohydride imidazolium ionic liquids, [IL]BH4, used for the first time as reductants in the N-formylation of various amines with CO2, provided an excellent yield of formamides. Under the same conditions, 5 bar CO2 and 80 °C, NaBH4 produced a mixture of N-formylated and N-methylated products in a ratio of 1 : 2. An alternative approach, based on the addition of halide imidazolium salts ([IL]Cl or [IL]Br) to the reactions of amine with NaBH4 and CO2, resulted in a significant increase of selectivity to formamide. However, no effect was noted for [IL]BF4 and [IL]PF6. Monitoring the reaction course in time using 1H NMR brought about new insight into the role of BH3 in the reduction of CO2 and the functionalization of amines. The formation of N-methylaniline - borane intermediate was evidenced.

Pd nanoparticles decorated on a porous Co(BDC-NH2) MOF as an effective heterogeneous catalyst for dye reduction

Herein, a new catalytic nanocomposite [Co(BDC-NH2)-Pd NPs] composed of a Co(BDC-NH2) MOF has been developed. The catalyst was prepared by modifying the synthesized porous Co(BDC-NH2) MOF with decorated Pd nanoparticles. This nanocatalyst was used as a heterogeneous catalyst in the reductive degradation of organic dyes Rhodamine B and methyl orange with NaBH4. The kinetic and thermodynamic parameters of the reactions were evaluated. The results showed that the low catalyst content could successfully catalyze the dye reduction reaction quickly (1 min). The metal-organic frameworks unique porous morphology of the Co(BDC-NH2) MOF appears to increase dye adsorption and achieve effective dye reduction. Additionally, recyclability studies of the catalyst confirmed that it could be recovered and reused for 10 consecutive reaction cycles with negligible Pd leaching and reduction in catalytic activity.

A Critical Review of Palladium Nanoparticles Decorated in Smart Microgels

Palladium nanoparticles (Pd) combined with smart polymer microgels have attracted significant interest in the past decade. These hybrid materials have unique properties that make them appealing for various applications in biology, environmental remediation, and catalysis. The responsive nature of the microgels in these hybrids holds great promise for a wide range of applications. The literature contains diverse morphologies and architectures of Pd nanoparticle-based hybrid microgels, and the architecture of these hybrids plays a vital role in determining their potential uses. Therefore, specific Pd nanoparticle-based hybrid microgels are designed for specific applications. This report provides an overview of recent advancements in the classification, synthesis, properties, characterization, and uses of Pd nanostructures loaded into microgels. Additionally, the report discusses the latest progress in biomedical, catalytic, environmental, and sensing applications of Pd-based hybrid microgels in a tutorial manner.

MOF-Incorporated Binuclear N-Heterocyclic Carbene-Cobalt Catalyst for Efficient Conversion of CO2 to Formamides

Environmental problem caused by carbon emission is of widespread concern. Involving CO₂ as C₁ resource into chemical synthesis is one of the most attractive ways for carbon recycling. Herein, the first example of host-guest composites featuring metal-organic framework (MOF)-encapsulated binuclear N-heterocyclic carbene (NHC) complex, Co₂ @MIL101, was developed with the molecularly dispersed [Co(IPr)Br]₂ (μ-Br)₂ (Co₂ ) loading in the cage of MIL-101(Cr) via a "ligand-in-dimer-trap" strategy, which was comprehensively investigated through various techniques including synchrotron X-ray absorption, electron microscopy, X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, and others. The noble-metal-free double-sites catalyst Co₂ @MIL101 exhibited promising stability, activity, efficiency, reusability, and substrate adaptability for converting CO₂ into various formamides with amines and hydrosilanes and achieved the best performance for one of the most useful formamides, N-methyl-N-phenylformamide (MFA), among the recyclable catalysts at ambient conditions, providing a reliable approach to successfully unify the advantages of both homo- and heterogeneous catalysts. Density functional theory calculations were applied to illustrate the superior activity of the binuclear NHC complex center as double-sites catalyst toward the activation of CO₂ .

Confinement synthesis in porous molecule-based materials: a new opportunity for ultrafine nanostructures

A balance between activity and stability is greatly challenging in designing efficient metal nanoparticles (MNPs) for heterogeneous catalysis. Generally, reducing the size of MNPs to the atomic scale can provide high atom utilization, abundant active sites, and special electronic/band structures, for vastly enhancing their catalytic activity. Nevertheless, due to the dramatically increased surface free energy, such ultrafine nanostructures often suffer from severe aggregation and/or structural degradation during synthesis and catalysis, greatly weakening their reactivities, selectivities and stabilities. Porous molecule-based materials (PMMs), mainly including metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and porous organic polymers (POPs) or cages (POCs), exhibit high specific surface areas, high porosity, and tunable molecular confined space, being promising carriers or precursors to construct ultrafine nanostructures. The confinement effects of their nano/sub-nanopores or specific binding sites can not only effectively limit the agglomeration and growth of MNPs during reduction or pyrolysis processes, but also stabilize the resultant ultrafine nanostructures and modulate their electronic structures and stereochemistry in catalysis. In this review, we highlight the latest advancements in the confinement synthesis in PMMs for constructing atomic-scale nanostructures, such as ultrafine MNPs, nanoclusters, and single atoms. Firstly, we illustrated the typical confinement methods for synthesis. Secondly, we discussed different confinement strategies, including PMM-confinement strategy and PMM-confinement pyrolysis strategy, for synthesizing ultrafine nanostructures. Finally, we put forward the challenges and new opportunities for further applications of confinement synthesis in PMMs.

Sustainable catalyst-free N-formylation using CO2 as a carbon source

The development of new sustainable catalytic conversion methods of carbon dioxide (CO2) is of great interest in the synthesis of valuable chemicals. N-formylation of CO2 with amine nucleophiles as substrates has been studied in depth. The key to benign formylation is to select a suitable reducing agent to activate CO2. This paper showcases the activation modes of CO2 and the construction strategies of sustainable and catalyst-free N-formylation systems. The research progress of catalyst-free N-formylation of amines and CO2 is reviewed. There are two broad prominent categories, namely reductive amidation of CO2 facilitated by organic solvents and ionic liquids in the presence of hydrosilane. Attention is also paid to discussing the involved reaction mechanism with practical applications and identifying the remaining challenges in this field.

Porous Organic Polymers for Catalytic Conversion of Carbon Dioxide

To overcome the challenges of global warming and environmental pollution, it is necessary to reduce the concentration of carbon dioxide (CO₂ ) in the atmosphere, which is mainly accumulated in the air through the burning of fossil fuels. Therefore, the development of environmentally friendly strategies to capture carbon dioxide and convert it into value-added products offers a promising way forward for reducing carbon dioxide concentration in the atmosphere. In this context, POPs (porous organic polymers) have shown great potential as CO₂ selective adsorbents due to their high specific surface area, chemical stability, nanoscale porosity and structural diversity, as well as POPs based heterogeneous catalysts for CO₂ conversion. This review provides a concise account of preparation methods of various POPs, challenges and current development trends of POPs in photocatalytic CO₂ reduction, electrocatalytic CO₂ reduction and chemical CO₂ conversion.

Nickel Nanoparticles Immobilized over Mesoporous SBA-15 for Efficient Carbonylative Coupling Reactions Utilizing CO2: A Spotlight

Ecofriendly routes for the synthesis of carbamates and carbonylative coupling products such as benzyl formate derivatives are very demanding for both academia and industries. Foreseeing a sustainable green future, we systematically analyzed the synthesis history of both these chemicals, mentioning their pros and cons. As a step towards green chemistry, here we have optimized the reaction conditions for the synthesis of various benzyl formates from corresponding benzyl halides and carbamates from substituted anilines and alkyl halides catalyzed by Ni(0) nanoparticles (NPs) immobilized over amine-functionalized ordered mesoporous SBA-15 material in the presence of CO₂ as C1 source. This spotlight on applications is aimed to provide a clear outlook to date regarding the gradual progress in the synthesis of both these aforementioned chemicals and finally addresses further efforts for overcoming the current challenges.

Effect of a modified 13X zeolite support in Pd-based catalysts for hydrogen oxidation at room temperature

This study investigated the effect of a modified 13X zeolite to Pd/zeolite catalyst on the oxidation of hydrogen to ensure safety from hydrogen leakage. The catalytic activity of Pd/zeolite catalysts was significantly affected by acid treatment of 13X zeolite support and various calcination temperatures (300 °C, 400 °C, 500 °C, 600 °C) of the Pd/zeolite catalyst. To understand the correlation between the activity and physical properties of the catalysts, activity test, XRD, BET, TEM, TPR, and TPO were performed; Pd/13X (400) was shown to have a high catalytic activity, which depended on the dispersion and particle size of palladium. Also, a strong PdH on the catalyst surface was formed, and a high catalytic activity at a low hydrogen concentration was obtained.

This study investigated the effect of a modified 13X zeolite to Pd/zeolite catalyst on the oxidation of hydrogen to ensure safety from hydrogen leakage.

A dual-functional urea-linked conjugated porous polymer anchoring silver nanoparticles for highly efficient CO2 conversion under mild conditions

A dual-functional urea-linked conjugated porous polymer (UCPP) assembled by enol-imine with ordered unit arrays that act as potential anchoring sites in the networks was fabricated, and was further applied as a support for Ag nanoparticles by the coordinate interaction between them. The UCPP not only can well confine the Ag particle size and facilitate high dispersion, but also can afford special CO₂-philic moieties to enhance the adsorption properties. The resulting Ag@UCPP as a heterogeneous catalyst exhibited excellent activity for the carboxylative cyclization of propargyl alcohols with CO₂ under mild conditions, together with good recyclability, which is probably attributed to the synergistic effect of the UCPP on the adsorption and activation of CO₂ and the immobilization of Ag nanoparticles. This work affords possible opportunities for the design and synthesis of a heterogeneous catalyst toward CO₂ conversion.

A facile route to transfer Cu nanoparticles to organic medium for better stabilization and improved photocatalytic activity towards N-formylation reaction

Cu nanoparticles were prepared in an aqueous phase by means of a simple reduction-route using sodium borohydride as the reducing agent in the presence of ascorbic acid and polyvinylpyrrolidone (PVP). The hydrosol of the Cu nanoparticles deteriorated within a day. It compelled to initiate a scheme to stabilize the nanoparticles for a long period of time. Phase transfer to organic solvents using Benzyldimethylstearylammonium chloride (BDSAC) as a phase transfer agent was found to be an effective path in this respect. BDSAC performed the dual role of dragging the Cu nanoparticles from water to organic solvent and also acted as a capping agent along with PVP for better stabilization of Cu nanoparticles. The organosol of the Cu nanoparticles exhibited excellent stability and promising catalytic activity towards N-formylation reactions on a number of amine substrates in presence of visible green LED light. The yield and reusability of the catalyst were promising. All the samples were thoroughly characterized by UV-visible spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, energy dispersive analysis of x-rays, x-ray photoelectron spectroscopy and thermo gravimetric analysis.

Recent advances in liquid hydrosilane-mediated catalytic N-formylation of amines with CO2

Carbon dioxide is an ideal raw material for the synthesis of complex organic compounds because of its rich, non-toxic, and good physical properties. It is of great significance to transform CO₂ into valuable fine chemicals and develop a green sustainable cycle of carbon surplus. Based on hydrosilane as a reducing agent, this work summarizes the recent applications of reductive amidation of CO₂ using different catalysts such as organocatalysts, ionic liquids (ILs), salts, transition metal complexes, and solvents. The main factors affecting the reductive amidation of CO₂ and the possible reaction mechanism are discussed. Moreover, the future orientation and catalytic systems of the formylation of amines with CO₂ and hydrosilane are prospected.

This review depicts different types of catalyst systems developed for upgrading of amines and carbon dioxide into N-formylated products in the presence of hydrosilane, with attention on reaction mechanism and process optimization.

Pyridine-based hypercrosslinked polymers as support materials for palladium photocatalysts and their application in Suzuki–Miyaura coupling reactions

Under ambient conditions, a Pd catalyst supported by a pyridine-based hypercrosslinked conjugated polymer shows excellent photocatalytic performance in S–M reactions.

Macroporous polystyrene degraded and functionalized chromium MPS-Cr(iii)-alen complex as a sustainable porous catalyst for CO2 fixation under atmospheric pressure and selective oxidation of aromatic alkenes

The benign synthesis of porous polystyrene supported chromium(iii) catalyst has been carried out for the production of cyclic carbonates via CO₂ fixation under atm. pressure and for the selective oxidation of aromatic alkenes under mild conditions.

Synthesis of benzimidazolones via CO2 fixation and N-phenyl formamides using formic acid in presence of zinc embedded polymer complex

A merrifield supported heterogeneous zinc catalyst [Zn(Meri-Ald-Py)] was synthesized and applied for benzimidazolone synthesis through the fixation of carbon dioxide (CO₂) and for different N-formylated products synthesis under mild reaction conditions.

Metal-Free N-Formylation of Amines with CO2 and Hydrosilane by Nitrogen-Doped Graphene Nanosheets

N-Formylation of amines with carbon dioxide (CO₂) as a carbonyl source is emerging as an important way for CO₂ transformation into high-value-added chemicals; however, the developed catalytic systems mainly focused on transition-metal-based homogeneous catalysts. Herein, we reported rationally designed nitrogen-doped graphene nanosheets (NG) as metal-free catalysts for N-formylation of various amines with CO₂ and hydrosilane to formamide under mild conditions. The NG catalyst displayed a wide amine scope with the desired formamide yields up to >99%, demonstrating its comparable catalytic performance to the reported transition-metal-based catalysts. Our experimental research reveals that the N-formylation of aniline involves an initial NG-promoted CO₂ hydrosilylation with PhSiH₃ to silyl formate and a subsequent nucleophilic attack of the aniline to give N-formanilide. Moreover, the key step of CO₂ hydrosilylation can be simplified to a pseudo-first-order reaction under a high CO₂ concentration with an observed reaction rate constant (k_obs) of 226 h^-1 at 40 °C and an apparent activation energy (E_a) of 34 kJ mol^-1. In sharp contrast, a k_obs of 23 h^-1 and E_a of 47 kJ mol^-1 were observed under catalyst-free conditions. Our theoretical investigation indicates that NG-promoted CO₂ hydrosilylation corresponds to an exergonic reaction (ΔG = -0.53 eV), which is much lower in energy state than that of catalyst-free conditions (ΔG = -0.44 eV). Finally, the NG showed outstanding recyclability in the N-formylation reaction with almost unchanged catalytic performance during twelve-time recycling. This research thus represented a breakthrough in metal-free transformation of CO₂ into fine chemicals with low-cost, environment-friendly, and carbon-based catalysts to replace the scarce and expensive transition-metal-based catalysts.

In2O3 Nanocrystals for CO2 Fixation: Atomic-Level Insight into the Role of Grain Boundaries

N-functionalization of amines with CO₂ and H₂ is one of the most important processes to make use of CO₂. Although noble metal-based catalysts with remarkable performance have been widely used in this process, developing efficient non-noble-metal-based catalysts remains a grand challenge. Herein, we report In₂O₃ nanocrystals with high density of grain boundaries (HGB-In₂O₃), which show excellent activity toward methylation of amines. Impressively, HGB-In₂O₃ achieved the optimal yield of 82.7% for N,N-dimethylaniline with a mass activity of 21.2 mmol·g^-1h^-1 in methylation of N-methylaniline, comparable to noble-metal-based catalysts. As a bonus, HGB-In₂O₃ held noticeable stability, remarkable selectivity, and comprehensive applicability. Further mechanistic studies revealed that the presence of high density of grain boundaries not only facilitated the adsorption and activation of CO₂ to generate CH₃OH as the intermediate but also enhanced the activation of N-H bond in amines, contributing to the attractive activity of HGB-In₂O₃ toward methylation of amines.

Pd NP-Decorated N-Rich Porous Organic Polymer as an Efficient Catalyst for Upgradation of Biofuels

Hydrodeoxygenation process is a potential route for upgrading biofuel intermediates, like vanillin, which is obtained in huge quantities through the chemical treatment of the abundant lignocellulosic biomass resources of nature, and this is attracting increasing attentions over the years. Herein, we report the grafting of palladium nanoparticles at the surface of porous organic polymer Pd-PDVTTT-1 synthesized through the co-condensation of 1,3,5-triallyl-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione and divinylbenzene in the presence of radical initiator under solvothermal reaction conditions. The Pd-PDVTTT-1 material has been characterized thoroughly by powder X-ray diffraction, nitrogen sorption, ultra-high-resolution transmission electron Microscopy, Fourier-transform infrared spectroscopy, ¹³C MAS NMR, and X-ray photoelectron spectroscopy analyses. High surface area together with good thermal stability of the Pd-PDVTTT-1 material has motivated us to explore its potential as heterogeneous catalyst in the hydrodeoxygenation of vanillin for the production of upgraded biofuel 2-methoxy-4-methylphenol in almost quantitative yield and high selectivity (94%).

Optimization of Process Variables in the Synthesis of Tributyl Citrate Using a Polyvinylpolypyrrolidone-Supported Brønsted Acidic Ionic Liquid Catalyst

A polyvinylpolypyrrolidone- (PVPP-) supported Brønsted acidic ionic liquid catalyst ([BsPVPP]HSO4) was synthesized by the reaction between SO3H-functionalized PVPP and H2SO4. The prepared catalyst was characterized by IR, XRD, FESEM, TG, and DSC. The catalytic activity of [BsPVPP]HSO4 in the preparation of tributyl citrate (TBC) by the esterification reaction between citric acid and n-butanol was investigated. Response surface methodology (RSM) was applied to optimize the process variables of the esterification reaction. The variables, including the reaction time, the n-butanol-to-citric acid mole ratio, the reaction temperature, and the catalyst amount, were optimized by a Box-Behnken design. Under optimized conditions, with a n-butanol-to-citric acid mole ratio of 5.2 : 1 and a reaction temperature of 120°C, the TBC yield reached 92.9% within 5.5 h in the presence of 6.6 wt% of catalyst; this result is in good agreement with the values predicted by the mathematical model. Moreover, the catalyst could be recycled four times with high catalytic activity.

One-pot selective N-formylation of nitroarenes to formamides catalyzed by core–shell structured cobalt nanoparticles

A first heterogeneous non-noble cobalt catalyst for one-pot direct N-formylation of nitroarenes exhibiting high activity with a broad substrate scope under mild conditions is synthesised. It is easily separated with good recyclability.