Magnetic yolk-shell structured periodic mesoporous organosilica supported palladium as a powerful and highly recoverable nanocatalyst for the reduction of nitrobenzenes

A novel palladium-loaded yolk-shell structured nanomaterial with magnetite core and phenylene-based periodic mesoporous organosilica (PMO) shell (Fe3O4@YS-Ph-PMO/Pd) nanocatalyst was synthesized for the reduction of nitrobenzenes. The Fe3O4@YS-Ph-PMO/Pd was prepared through cetyltrimethylammonium bromide (CTAB) directed condensation of 1,4-bis(triethoxysilyl)benzene (BTEB) around Fe3O4@silica nanoparticles followed by treatment with palladium acetate. This nanocatalyst was characterized by using Fourier transform infrared (FT-IR) spectroscopy, thermal gravimetric analysis (TGA), low-angle and wide-angle powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) analyses. These analyses showed a magnetic nanomaterial with high chemical and thermal stability for the designed composite. The Fe3O4@YS-Ph-PMO/Pd nanocomposite was employed as a powerful and highly recoverable catalyst in the green reduction of nitroarenes in H2O at room temperature. A variety of nitroarene derivatives were applied as substrate in the presence of 0.9 mol% of Fe3O4@YS-Ph-PMO/Pd catalyst. All nitroarenes were selectively converted to their corresponding amines with high to excellent yields (92-96%) within short reaction times (10-18 min). This catalyst was recovered and reused at least 11 times without significant decrease in efficiency and stability.

Highly dispersed rhodium atoms supported on defect-rich Co(OH)2 for the chemoselective hydrogenation of nitroarenes

0.54% Rh/Co(OH)2 exhibited 100% selectivity for –NO2 hydrogenation at >96% conversion for nitroarene hydrogenation. Its excellent catalytic performance is due to the interfacial effect of Rh–Co(OH)2 and Rh in the form of single atoms and nanoclusters.

Pd Doped on TCH@SBA-15 Nanocomposites: Fabrication and Application as a New Organometallic Catalyst in the Three-Component Synthesis of N-Benzo-imidazo- or -thiazole-1,3-thiazolidinones

In this study, Pd(II)/TCH@SBA-15 nanocomposites were synthesized by the grafting of 3-chloropropyltriethoxysilane and thiocarbohydrazide on SBA-15 and subsequent deposition of palladium acetates through the ligand-metal coordination method. The structure and morphology of this nanoporous nanocomposite was thoroughly identified by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, atomic absorption spectroscopy, and Brunauer-Emmett-Teller instrumental analyses. Furthermore, the catalytic activity of this nanocomposite was investigated in the three-component synthesis of 3-benzimidazolyl or benzothiazoleyl-1,3-thiazolidin-4-ones via a reaction of 2-aminobenzimidazole or 2-aminobenzothiazole, aromatic aldehydes, and thioglycolic acid in an acetone-H2O mixture under green conditions. The Pd/TCH@SBA-15 nanocatalyst is demonstrated to exhibit a high catalyzing activity in the three-component reaction of the synthesis of N-heterocyclic thiazolidinones with good to excellent yields. One of the advantages of the suggested method is the direct application of the thiocarbohydrazide ligand to stabilize Pd nanoparticles through formation of a stable ring complex without creating an additional Schiff base step. Moreover, this organometallic nanocatalyst can be recycled several times with no notable leaching or loss of performance.

Cu@Pd/C with Controllable Pd Dispersion as a Highly Efficient Catalyst for Hydrogen Evolution from Ammonia Borane

A series of Cu@Pd/C with different Pd contents was prepared using the galvanic reduction method to disperse Pd on the surface of Cu nanoparticles on Cu/C. The dispersion of Pd was regulated by the Cu(I) on the surface, which was introduced by pulse oxidation. The Cu₂O did not react during the galvanic reduction process and restricted the Pd atoms to a specific area. The pulse oxidation method was demonstrated to be an effective process to control the oxidization degree of Cu on Cu/C and then to govern the dispersion of Pd. The catalysts were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscope (HRTEM), high angular annular dark field scanning TEM (HAADF-STEM), energy-dispersive spectroscopy (EDS) mapping, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), and inductively coupled plasma optical emission spectrometer (ICP-OES), which were used to catalyze the hydrogen evolution from ammonia borane. The Cu@Pd/C had much higher activity than the PdCu/C, which was prepared by the impregnation method. The TOF increased as the Cu₂O in Cu/C used for the preparation of Cu@Pd/C increased, and the maximum TOF was 465 mol_H2 min^-1 mol_Pd^-1 at 298 K on Cu@Pd_0.5/C-640 (0.5 wt % of Pd, 640 mL of air was pulsed during the preparation of Cu/C-640). The activity could be maintained in five continuous processes, showing the strong stability of the catalysts.

Sodium alginate passivated CuInS2/ZnS QDs encapsulated in the mesoporous channels of amine modified SBA 15 with excellent photostability and biocompatibility

We herein report the synthesis of CuInS₂/ZnS (CIS/ZnS) quantum dots (QDs) via a greener method followed by sodium alginate (SA) passivation and encapsulation into mesoporous channels of amine modified silica (SBA15-NH₂) for improved photostability and biocompatibility. The as-synthesized CIS/ZnS QDs exhibited near infrared emission even after SA passivation and silica encapsulation. Transmission electron microscopy (TEM) and Small angle X-ray diffraction (XRD) revealed the mesoporous nature of the SBA-15 remained stable after loading with the SA-CIS/ZnS QDs. The effective encapsulation of SA-CIS/ZnS QDs inside the pores of SBA15-NH₂ matrix was confirmed by Brunauer-Emmett-Teller (BET) pore volume analysis while the interaction between the QDs and SBA15-NH₂ was confirmed using Fourier transform infrared (FTIR) spectroscopy. The photostability of the QDs was greatly enhanced after these modifications. The resultant SA-CIS/ZnS-SBA15-NH₂ (QDs-silica) composite possessed remarkable biocompatibility towards lung cancer (A549) and kidney (HEK 293) cell lines making it a versatile material for theranostic applications.

Preparation of 1-Hydroxy-2,5-hexanedione from HMF by the Combination of Commercial Pd/C and Acetic Acid

The development of a simple and durable catalytic system for the production of chemicals from a high concentration of a substrate is important for biomass conversion. In this manuscript, 5-hydroxymethylfurfural (HMF) was converted to 1-hydroxy-2,5-hexanedione (HHD) using the combination of commercial Pd/C and acetic acid (AcOH) in water. The influence of temperature, H₂ pressure, reaction time, catalyst amount and the concentration of AcOH and HMF on this transformation was investigated. A 68% yield of HHD was able to be obtained from HMF at a 13.6 wt% aqueous solution with a 98% conversion of HMF. The resinification of intermediates on the catalyst was characterized to be the main reason for the deactivation of Pd/C. The reusability of the used Pd/C was studied to find that most of the activity could be recovered by being washed in hot tetrahydrofuran.

Facile Preparation of Pd/UiO-66-v for the Conversion of Furfuryl Alcohol to Tetrahydrofurfuryl Alcohol under Mild Conditions in Water

The hydrogenation of furan ring in the biomass-derived furans is of great importance for the conversion of biomass to valuable chemicals. Fabrication of high activity and selectivity catalyst for this hydrogenation under mild conditions was one of the focuses of this research. In this manuscript, UiO-66-v, in which vinyl bonded to the benzene ring, was first prepared. Then, the uniformly distributed vinyl was used as the reductant for the preparation of Pd/UiO-66-v. The catalyst was characterized by X-ray diffraction, thermogravimetric, N₂ physical adsorption/desorption, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscopy, energy dispersive spectrometer elemental mappings, and inductively coupled plasma atomic emission spectroscopy to find the Pd/UiO-66-v had a narrow palladium nanoparticles size of 3–5 nm and maintained the structure and thermal stability of UiO-66-v. The Pd/UiO-66-v was used for the hydrogenation of furfuryl alcohol to tetrahydrofurfuryl alcohol in water. 99% conversion of furfuryl alcohol was obtained with 90% selectivity to tetrahydrofurfuryl alcohol after reacted at 0.5 MPa H₂, 303 K for 12 h. The Pd/UiO-66-v was proved to be effective for the hydrogenation of furan ring in furans and could be used for at least five times.

Functionalized Silicas for Metal-Free and Metal-Based Catalytic Applications: A Review in Perspective of Green Chemistry

Heterogeneous catalysis plays a key role in promoting green chemistry through many routes. The functionalizable reactive silanols highlight silica as a beguiling support for the preparation of heterogeneous catalysts. Metal active sites anchored on functionalized silica (FS) usually demonstrate the better dispersion and stability due to their firm chemical interaction with FSs. Having certain functional groups in structure, FSs can act as the useful catalysts for few organic reactions even without the need of metal active sites which are termed as the covetous reusable organocatalysts. Magnetic FSs have laid the platform where the effortless recovery of catalysts is realized just using an external magnet, resulting in the simplified reaction procedure. Using FSs of multiple functional groups, we can envisage the shortened reaction pathway and, reduced chemical uses and chemical wastes. Unstable bio-molecules like enzymes have been stabilized when they get chemically anchored on FSs. The resultant solid bio-catalysts exhibited very good reusability in many catalytic reactions. Getting provoked from the green chemistry aspects and benefits of FS-based catalysts, we confer the recent literature and progress focusing on the significance of FSs in heterogeneous catalysis. This review covers the preparative methods, types and catalytic applications of FSs. A special emphasis is given to the metal-free FS catalysts, multiple FS-based catalysts and magnetic FSs. Through this review, we presume that the contribution of FSs to green chemistry can be well understood. The future perspective of FSs and the improvements still required for implementing FS-based catalysts in practical applications have been narrated at the end of this review.

Calixarene-Assisted Pd Nanoparticles in Organic Transformations: Synthesis, Characterization, and Catalytic Applications in Water for C-C Coupling and for the Reduction of Nitroaromatics and Organic Dyes

A new type of ternary hybrid, Pd@MCM-Calix_ox, based on mesoporous silica, calixarene conjugate, and Pd(0) nanoparticles (NPs) was synthesized by sacrificial oxidation of allylic calixarene conjugate eventually functionalized with mesoporous silica without using any external reducing agent. The role of the calix conjugate in the formation of Pd@MCM-Calix_ox has been established. The hybrid, Pd@MCM-Calix_ox, was characterized by different techniques to support the formation of well-dispersed Pd(0) NPs of 12 ± 2 nm size. The catalyst, Pd@MCM-Calix_ox, has been proven to be a resourceful one in water in three different types of reactions, namely, Suzuki C-C cross coupling, reduction of both hydrophilic and hydrophobic nitroaromatic compounds, and reduction and degradation of cationic, anionic, and neutral organic dyes. The catalyst exhibited higher turnover frequencies for all these transformations even when a very low concentration of Pd-based catalyst was used. The Pd@MCM-Calix_ox hybrid catalyst can be recycled several times without experiencing any significant loss in the activity. Also, the regenerated catalyst showed retention of well-spread Pd(0) species even after several catalytic cycles. The tetraallyl calixarene, allylCalix, conjugate acts as a reducing agent, also controls the size, and yields the well-dispersed Pd(0) NPs. The calix conjugate further provides a hydrophobic core in assisting the diffusion of hydrophobic substrates toward catalytic sites.

Long-Range Olefin Isomerization Catalyzed by Palladium(0) Nanoparticles

Long-range olefin isomerization of 2-alkenylbenzoic acid derivatives going through two to five sp³-carbon atoms to give (E)-alkenes was achieved with palladium(0) nanoparticles. The substrate scope of this reaction includes carboxylic acid, ester, and primary to tertiary amides and tolerates various substituents on the benzene ring. This isomerization reaction was catalyzed by recyclable Pd(0) nanoparticles, prepared in situ from PdCl₂ and characterized by X-ray powder diffraction and scanning electron microscopy analyses. ¹H NMR studies and kinetic modeling supported a stepwise process. This new process was applied to synthesize a natural dihydroisocoumarin with good efficiency.