Ultra-fine Pd nanoparticles confined in a porous organic polymer: A leaching-and-aggregation-resistant catalyst for the efficient reduction of nitroarenes by NaBH4

Highly efficient catalytic transfer hydrogenation for the conversion of nitrobenzene to aniline over PdO/TiO2: The key role of in situ switching from PdO to Pd

The reduction of nitrobenzene to aniline is very important for both pollution control and chemical synthesis. Nevertheless, difficulties still remain in developing a catalytic system having high efficiency and selectivity for the production of aniline. Herein, it was found that PdO nanoparticles highly dispersed on TiO2 support (PdO/TiO2) functioned as a highly efficient catalyst for the reduction of nitrobenzene in the presence of NaBH4. Under favorable conditions, 95% of the added nitrobenzene (1 mmol/L) was reduced within 1 min with an ultra-low apparent activation energy of 10.8 kJ/mol by using 0.5%PdO/TiO2 as catalysts and 2 mmol/L of NaBH4 as reductants, and the selectivity to aniline even reached up to 98%. The active hydrogen species were perceived as dominant species during the hydrogenation of nitrobenzene by the results of isotope labeling experiments and ESR spectroscopic. A mechanism was proposed as follows: PdO activates the nitro groups and leads to in-situ generation of Pd, and the generated Pd acts as the reduction sites to produce active hydrogen species. In this catalytic system, nitrobenzene prefers to be adsorbed on the PdO nanoparticles of the PdO/TiO2 composite. Subsequently, the addition of NaBH4 results in in-situ generation of a Pd/PdO/TiO2 composite from the PdO/TiO2 composite, and the Pd nanoclusters would activate NaBH4 to generate active hydrogen species to attack the adsorbed nitro groups. This work will open up a new approach for the catalytic transfer hydrogenation of nitrobenzene to aniline in green chemistry.

An Overview of Heterogeneous Catalysts Based on Hypercrosslinked Polystyrene for the Synthesis and Transformation of Platform Chemicals Derived from Biomass

Platform chemicals, also known as chemical building blocks, are substances that serve as starting materials for the synthesis of various value-added products, which find a wide range of applications. These chemicals are the key ingredients for many fine and specialty chemicals. Most of the transformations of platform chemicals are catalytic processes, which should meet the requirements of sustainable chemistry: to be not toxic for humans, to be safe for the environment, and to allow multiple reuses of catalytic materials. This paper presents an overview of a new class of heterogeneous catalysts based on nanoparticles of catalytically active metals stabilized by a polymer matrix of hypercrosslinked polystyrene (HPS). This polymeric support is characterized by hierarchical porosity (including meso- and macropores along with micropores), which is important both for the formation of metal nanoparticles and for efficient mass transfer of reactants. The influence of key parameters such as the morphology of nanoparticles (bimetallic versus monometallic) and the presence of functional groups in the polymer matrix on the catalytic properties is considered. Emphasis is placed on the use of this class of heterogeneous catalysts for the conversion of plant polysaccharides into polyols (sorbitol, mannitol, and glycols), hydrogenation of levulinic acid, furfural, oxidation of disaccharides, and some other reactions that might be useful for large-scale industrial processes that aim to be sustainable. Some challenges related to the use of HPS-based catalysts are addressed and multiple perspectives are discussed.

Efficient Reduction in Methylene Blue Using Palladium Nanoparticles Supported by Melamine-Based Polymer

In this work, palladium nanoparticles, supported by polyaminals (Pd@PAN-NA), were synthesized via a reverse double solvent approach and used as a nano catalyst. The thermogravimetric and the elemental analysis revealed that the catalyst had good dispersity and improved thermal stability. The catalytic activity of the prepared Pd@PAN-NA catalyst was studied for a methylene blue chemical reaction in the presence of NaBH4 as a reducing agent. The effect of the catalyst dose, pH, and dye initial concentration were examined to optimize the chemical reduction conditions. The prepared catalyst Pd@PAN-NA removed 99.8% of methylene blue organic dye, indicating its potential effect for treating waste and contaminated water.

Naphthalene-Based Polymers as Catalytic Supports for Suzuki Cross-Coupling

In this work, for the first time, naphthalene (NA)-based polymers were synthesized by one-stage Friedel-Crafts crosslinking. The influence of NA functionalization by -OH, -SO₃H, and -NO₂ groups on the polymers' porosity and distribution of the catalytically active phase (Pd) was studied. Synthesized catalytic systems containing 1 wt.% of Pd either in the form of Pd(II) species or Pd(0) nanoparticles supported on NA-based polymers were tested in a model reaction of Suzuki cross-coupling between 4-bromoanisole and phenylboronic acid under mild reaction conditions (60 °C, ethanol-water mixture as a solvent). These novel catalysts demonstrated high efficiency with more than 95% of 4-bromoanisole conversion and high selectivity (>97%) for the target 4-methoxybiphenyl.

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.

Single-ion chelation strategy for synthesis of monodisperse Pd nanoparticles anchored in MOF-808 for highly efficient hydrogenation and cascade reactions

Ultrafine Pd nanoparticles are prepared using a single-ion precursor on a MOF-808 carrier. The ligand 2,3-pyrazinedicarboxylic acid (Pza) is dispersed in porous MOF-808 via grafting on formic acid sites, and thus Pd²⁺ ions are chelated by Pza to form a new single-ion precursor Pd@MOF-808-Pza. Then a Pd-nano@MOF-808-Pza catalyst is prepared by direct reduction of this precursor using NaBH₄. Material characterization reveals the homogeneous dispersion of 3-6 nm Pd nanoparticles within the MOF-808 matrix. Pd-nano@MOF-808-Pza exhibits excellent catalytic activity in the hydrogenation of unsaturated nitrogen-containing compounds, and other typical reactions, such as the Knoevenagel condensation, Suzuki/Heck cross-coupling, and hydrogen tandem reactions. In addition, density functional theory (DFT) calculations are carried out to elucidate the chelation of Pd²⁺ ions by Pza on MOF-808 and propose mechanisms of hydrogenation reactions. This work provides an effective reduction catalyst, and more importantly, a single-ion chelation strategy for design and synthesis of metal supported catalysts.

Ultrafine and well-dispersed Pd-Ni bimetallic catalyst stabilized by dendrimer-grafted magnetic graphene oxide for selective reduction of toxic nitroarenes under mild conditions

A facile and efficient strategy is introduced for growing a dendrimer structure on the surface of magnetic graphene oxide by using thiol-ene click reaction. The as-synthesized dendrimer-grafted magnetic graphene oxide was used as a suitable support for bimetallic Pd-Ni nanoparticles. The prepared nanocomposite was utilized for the reduction of toxic nitroarenes to aminoarenes by using sodium borohydride in aqueous medium at room temperature. Various nitroarenes with functional groups like nitrile, halogen, carbonyl, hydroxyl, acid, and heterocycles were converted to their corresponding anilines with good to excellent yields. The enhanced performance of the catalyst could be attributed to the synergistic effect between Ni and Pd which causes the reaction to proceed more efficiently. Moreover, the catalyst could be readily isolated from the reaction mixture by utilizing an external magnet and reused till 5th cycles with marginal loss of activity.

Mono- and Bimetallic Nanoparticles Stabilized by an Aromatic Polymeric Network for a Suzuki Cross-Coupling Reaction

This work addresses the Suzuki cross-coupling between 4-bromoanisole (BrAn) and phenylboronic acid (PBA) in an environmentally benign ethanol-water solvent catalysed by mono- (Pd) and bimetallic (PdAu, PdCu, PdZn) nanoparticles (NPs) stabilised within hyper-cross-linked polystyrene (HPS) bearing tertiary amino groups. Small Pd NPs of about 2 nm in diameters were formed and stabilized by HPS independently in the presence of other metals. High catalytic activity and complete conversion of BrAn was attained at low Pd loading. Introduction of Zn to the catalyst composition resulted in the formation of Pd/Zn/ZnO NPs, which demonstrated nearly double activity as compared to Pd/HPS. Bimetallic core-shell PdAu/HPS samples were 3-fold more active as compared to Pd/HPS. Both Pd/HPS and PdAu/HPS samples revealed promising stability confirmed by catalyst recycling in repeated reaction runs.

Superhydrophilic three-dimensional porous spent coffee ground reduced palladium nanoparticles for efficient catalytic reduction

The use of functional biodegradable wastes to treat environmental problems would create minimal extra burden to our environment. In this paper, we propose a sustainable and practical strategy to turn spent coffee ground (SCG) into a multifunctional palladium-loaded catalyst for water treatment instead of going into landfill as solid waste. Bleached delignified coffee ground (D-SCG) has a porous structure and a good capability to reduce Pd (II) to Pd (0). A large amount of nanocellulose is formed on the surface of SCG after bleaching by H₂O₂, which anchors and disperses the palladium nanoparticles (Pd NPs). The D-SCG loaded with Pd NPs (Pd-D-SCG) is superhydrophilic, which facilitates water transport and thus promotes efficient removal of organic pollutants dissolved in water. Pd-D-SCG exhibits excellent room temperature catalytic activity for the removal of 4-nitrophenol (4-NP) and methylene blue (MB) in water and shows good chemical stability and recyclability in water, with no obvious decrease even after five repeated cycles.

Nickel hydroxide nanoparticles decorated napthalene sulfonic acid-doped polyaniline nanotubes as efficient catalysts for nitroarene reduction

Nanosize nickel hydroxide decorated 2-napthalene sulfonic acid-doped polyaniline nanotubes nanocomposites (Ni(OH)₂@NSA-PANI NCs) were successfully developed for the catalytic reduction of aromatic nitro compounds. The Ni(OH)₂@NSA-PANI NCs were synthesised by depositing Ni(OH)₂ nanoparticles onto 2-napthalene sulfonic acid doped PANI nanotubes surface. The resulting material was characterized using field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (P-XRD), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The prepared nanocomposite showed a remarkable ability to catalytically hydrogenate aromatic nitro compounds using sodium borohydride (NaBH₄) as hydrogen source in aqueous medium at room temperature. Kinetic studies were performed using 4-nitrophenol (4-NP) as the model substrate, using the Langmuir-Hinshelwood model. The catalyst showed pseudo-first-order kinetics, with rate constants estimated between 0.08287 and 0.3649 min^-1. Catalyst recyclability without reduced activity was demonstrated over 10 successive cycles. The optimised nanocomposite catalyst demonstrated a low activation energy barrier towards 4-NP reduction.

Rapid iodine adsorption from vapor phase and solution by a nitrogen-rich covalent piperazine–triazine-based polymer

The excellent pore performance and high nitrogen content of n-CTP result in increased diffusion and adsorption of I₂, which subsequently decreases the equilibrium time.

Amino-Modified Silica as Effective Support of the Palladium Catalyst for 4-Nitroaniline Hydrogenation

The article describes the synthesis of aminoorgano-functionalized silica as a prospective material for catalysis application. The amino groups have electron donor properties which are valuable for the metal chemical state of palladium. Therefore, the presence of electron donor groups is important for increasing catalysts’ stability. The research is devoted to the investigation of silica amino-modified support influence on the activity and stability of palladium species in 4-nitroaniline hydrogenation process. A series of catalysts with different supports such as SiO2, SiO2-C3H6-NH2 (amino-functionalized silica), γ-Al2O3 and activated carbon were studied. The catalytic activity was studied in the hydrogenation of 4-nitroaniline to 1,4-phenylenediamine. The catalysts were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and chemisorption of hydrogen by the pulse technique. The 5 wt.% Pd/SiO2-C3H6-NH2 catalyst exhibited the highest catalytic activity for 4-nitroaniline hydrogenation with 100% conversion and 99% selectivity with respect to 1,4-phenylenediamine.

Ultrafine Rh nanoparticles confined by nitrogen-rich covalent organic frameworks for methanolysis of ammonia borane

An Rh/PC-COF was synthesized using a metal–nitrogen coordination reduction strategy and was applied as a highly efficient catalyst for methanolysis of ammonia borane.

Pd nanoparticles stabilized with phosphine-functionalized porous ionic polymer for efficient catalytic hydrogenation of nitroarenes in water

Small palladium nanoparticles stabilized with phosphine-functionalized PIP displayed high catalytic activity for nitroarenes hydrogenation. Nano-size Pd particles, electron-donation effect of phosphine ligand, and surface wettability account for its excellent catalytic performance.