A novel Ag-loaded 4 Å zeolite as an efficient catalyst for epoxidation of styrene

In this study, a novel Ag-loaded 4 Å zeolite was synthesized through the combined action of strong ultrasound and a high-voltage electrostatic field (the Z-Ag-UE) and its catalytic activity was evaluated in the epoxidation of styrene. The prepared catalysts were characterized using XRD, SEM, XPS, BET, TG, ICP-OES. The results showed that the silver evenly dispersed inside the octahedral 4 Å zeolite structure rather than being attached to the surface of the material like in the impregnation method, and this Ag-loaded 4 Å zeolite had a high surface area, uniform particle size distribution, and excellent high temperature thermal stability. The catalytic performance of the Ag-loaded 4 Å zeolite was investigated by varying the reaction conditions such as the amount of catalyst, temperature, and reaction time. Under optimized conditions, the Ag-loaded 4 Å zeolite showed high selectivity and conversion for the epoxidation of styrene, achieving a conversion rate of up to 98% and a selectivity of 94%. In particular, the catalyst had excellent recyclability and was reused more than fifteen times with the catalytic performance remaining unchanged. This method of loading metal prepared under external field conditions provides a new method and idea for future research in related fields.

Immobilization of Ni(ii) complex on the surface of mesoporous modified-KIT-6 as a new, reusable and highly efficient nanocatalyst for the synthesis of tetrazole and pyranopyrazole derivatives

In this paper, KIT-6@SMTU@Ni was successfully synthesized via a new method of Ni(ii) complex stabilization on modified mesoporous KIT-6, as a novel and green heterogeneous catalyst. The obtained catalyst (KIT-6@SMTU@Ni) was characterized using Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) calculation, X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), energy-dispersive X-ray spectroscopy (EDS), X-ray mapping, thermogravimetric analysis (TGA) techniques and scanning electron microscopy (SEM). After complete characterization of the catalyst, it was successfully used for the synthesis of 5-substituted 1H-tetrazoles and pyranopyrazoles. Moreover, tetrazoles were synthesized from benzonitrile derivatives and sodium azide (NaN₃). All tetrazole products were synthesized with high TON, TOF and excellent yields (88-98%) in a reasonable time (0.13-8 h), demonstrating the efficiency and practicality of the KIT-6@SMTU@Ni catalyst. Furthermore, pyranopyrazoles were prepared through the condensation reaction of benzaldehyde derivatives with malononitrile, hydrazine hydrate and ethyl acetoacetate with high TON, TOF and excellent yields (87-98%) at appropriate times (2-10.5 h). KIT-6@SMTU@Ni could be reused for five runs without any re-activation. Significantly, this plotted protocol has prominent benefits, such as applying green solvents, the use of commercially available and low-cost materials, excellent separation and reusability of the catalyst, short reaction time, high yield of products and a facile work-up.

Self-Assembly of a Pd4Cu8L8 Cage for Epoxidation of Styrene and Its Derivatives

Herein we report a discrete heterometallic Pd₄Cu₈L₈ cage with a tubular structure, which was synthesized by the assembly of copper metalloligands and Pd^II ions in a stepwise manner. The Pd₄Cu₈L₈ cage has been unequivocally characterized by single-crystal X-ray diffraction, electrospray ionization-mass spectroscopy, and energy dispersive spectroscopy. The cage showed excellent catalytic activity in the epoxidation of styrene and its derivatives under conditions without using additional solvent, providing potential material for catalyzing the oxidation reactions.

Copper-complexed dipyridyl-pyridazine functionalized periodic mesoporous organosilica as a heterogeneous catalyst for styrene epoxidation

A new heterogeneous catalyst has been synthesized by immobilization of a copper complex on dipyridyl-pyridazine functionalized periodic mesoporous organosilica (dppz-vPMO). This ordered support was first prepared by a co-condensation reaction between vinyltriethoxysilane and 1,2-bis(trimethoxysilyl)ethane and further post-functionalized through a hetero Diels-Alder reaction with 3,6-di-2-pyridyl-1,2,4,5-tetrazine. Techniques such as XRD, N₂ isotherms, TEM, ¹³C NMR, XPS and DRIFT, among others, were employed to characterize the surface functionalized materials. These results have proven the ordered mesostructure of the materials as well as the presence of novel nitrogen-chelating heterocyclic compounds on the pore surface after the post-modification process. Additionally, the successful anchoring of a copper complex on the dipyridyl-pyridazine (dppz) ligands has been confirmed. The resulting material was evaluated as a heterogeneous catalyst in the epoxidation of styrene using tert-butylhydroperoxide (TBHP) as an oxidant. Under the optimized reaction conditions, Cu@dppz-vPMO showed a high styrene conversion (86.0%) and a remarkable selectivity to styrene oxide (41.9%). Indeed, this catalyst provided excellent catalytic results in terms of stability, reaction rate, conversion and selectivity compared to other bipyridine-like copper catalysts.

Synthesis of nanoscale CuO via precursor method and its application in the catalytic epoxidation of styrene

Nanoscale CuO with diameters in the range of 7–8 nm has been synthesized via a two-step precipitation–calcination method using copper(ii) isonicotinate tetrahydrate as the precursor. The first step involves the room temperature stirring of an alkaline ethanolic solution of the precursor which gives a non-crystalline CuO species, while the second step involves the calcination of the product of the first step at 180 °C to form nanocrystalline CuO which has been characterized by PXRD, TEM, SEM, H₂-TPR and Raman spectroscopy, etc. The CuO material has shown excellent catalytic activity in the oxidation of styrene using TBHP as the oxidizing agent leading to complete styrene conversion with more than 95% styrene oxide selectivity at the end of 6 h. The oxide catalyst can be reused for at least 6 successive runs without significant loss in activity.

Nanoscale CuO with diameters in the range of 7–8 nm has been synthesized via a two-step precipitation–calcination method using copper(ii) isonicotinate tetrahydrate as the precursor.

Syntheses, characterization and properties of two new dodeca-niobates presenting unprecedented features

Two new dodeca-niobate materials, K3[Nb2O2][H7SiNb12O40]·16H2O (1) and [Cu(en)2]9[(VNb12V1.69Nb0.31O42en0.31)2]·20.69H2O (2) (en = ethylenediamine), have been obtained under hydrothermal conditions and characterized by IR, UV-Vis, XRD, and single crystal X-ray diffraction analysis. Single crystal X-ray analysis reveals that compound 1 presents a reasonable bridging layer structure model and that K plays a great role in the three-dimensional structure. Compound 2 is the first capped Keggin POM with organic ligand chelating the capping atom. The photocatalytic hydrogen evolution and styrene epoxidation catalytic properties of the two compounds were also assessed. Additionally, compound 1 is also a good photocatalyst to degrade RhB.

Cu(ii)Cl2 containing bispyridine-based porous organic polymer support prepared via alkyne–azide cycloaddition as a heterogeneous catalyst for oxidation of various olefins

A new type of porous organic polymer (POP) based heterogeneous catalyst Cu-POP was prepared by immobilizing Cu(ii)Cl₂ into bpy containing POP prepared via alkyne–azide cycloaddition. It showed good catalytic oxidations towards various olefins.

Fur-Imine-Functionalized Graphene Oxide-Immobilized Copper Oxide Nanoparticle Catalyst for the Synthesis of Xanthene Derivatives

Fur-imine-functionalized graphene oxide-immobilized copper oxide nanoparticles (Cu(II)-Fur-APTES/GO) are synthesized and found to be a cost-effective, efficient, and reusable heterogeneous nanocatalyst for the preparation of pharmaceutically important xanthene derivatives under greener solvent conditions. Cu(II)-Fur-APTES/GO exhibits excellent result in the synthesis of xanthenes with reduced reaction time (25-50 min) and higher yields (up to 95%) and has a simple procedure, ease of product separation, and no byproducts. Moreover, the nanocatalyst has a Cu loading of 13.5 at. % over functionalized GO which is far superior than the already known metal-based heterogeneous catalysts. The newly synthesized catalyst has been characterized by various physiochemical techniques such as X-ray photoelectron spectroscopy, X-ray diffraction, energy-dispersive X-ray, Raman spectroscopy for structural characterization, field emission scanning electron microscopy and high-resolution transmission electron microscopy for morphological characterization. The catalyst showed admirable recyclability up to five consecutive runs, and there was no appreciable loss in catalytic efficiency.

Effects of alumina on GO and KIT-6 supports for the acetylation of glycerol

The support effects of graphene oxide (GO) and KIT-6 on alumina loading as a catalyst to convert glycerol into value added products via the acetylation reaction were studied.

Preparation of a bispyridine based porous organic polymer as a new platform for Cu(ii) catalyst and its use in heterogeneous olefin epoxidation

A new type of bispyridine (bpy) incorporated POP was prepared via a cobalt-catalyzed acetylene trimerization. Subsequent metalation of CuCl₂ gave POP-Cu(ii) which displayed outstanding olefin oxidation activity.

Two-Dimensional Imine-Linked Covalent Organic Frameworks as a Platform for Selective Oxidation of Olefins

Two-dimensional imine-linked covalent organic frameworks with hydroxyl groups, TAPT-DHTA-COF_HX and TAPT-DHTA-COF_DMF, were respectively constructed by the condensation of 1,3,5-tris-(4-aminophenyl)triazine and 2,5-dihydroxyl-terephthalaldehyde under solvothermal and reflux conditions. Both COFs possess excellent thermal stability and a similar eclipsed stacking structure verified by XRD patterns. However, TAPT-DHTA-COF_HX presented a larger surface area (2238 m²/g) and higher crystallinity than TAPT-DHTA-COF_DMF. Significantly, copper ions are efficiently incorporated into the pores of these two COFs via the coordination interaction with hydroxyl groups and imine linkers. The obtained copper-containing COFs (Cu-COF_HX and Cu-COF_DMF) were employed in the selective oxidation of styrene to benzaldehyde. Cu-COF_HX with superior surface area (1886 m²/g) and pore volume (1.11 cm³/g) exhibited excellent catalytic performance and recyclability. This strategy not only provides a convenient approach to design imine-linked 2D COFs with hydroxyl groups, but also develops their novel application for catalysis.

Quantum size effect and catalytic activity of nanosized single-crystalline spherical β-Ga2O3 particles by thermal annealing of liquid metal nanoparticles

Nanosized single-crystalline spherical β-Ga₂O₃ particles were readily prepared from liquid metal gallium.

Synthesis of a highly dispersed CuO catalyst on CoAl-HT for the epoxidation of styrene

Non-noble CuO/CoAl-HT catalyst with high dispersion and rich electronic density exhibits excellent catalytic performance for the epoxidation of styrene.

A series of organic–inorganic hybrid compounds formed by [P2W18O62]6−and several types of transition metal complexes

A series of new organic–inorganic hybrid compounds based on [P₂W₁₈O₆₂]⁶⁻and several types of transition metal complexes have been synthesized and characterized.

Quantitative analysis of flavanones from citrus fruits by using mesoporous molecular sieve-based miniaturized solid phase extraction coupled to ultrahigh-performance liquid chromatography and quadrupole time-of-flight mass spectrometry

An analytical procedure based on miniaturized solid phase extraction (SPE) and ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry was developed and validated for determination of six flavanones in Citrus fruits. The mesoporous molecular sieve SBA-15 as a solid sorbent was characterised by Fourier transform-infrared spectroscopy and scanning electron microscopy. Additionally, compared with reported extraction techniques, the mesoporous SBA-15 based SPE method possessed the advantages of shorter analysis time and higher sensitivity. Furthermore, considering the different nature of the tested compounds, all of the parameters, including the SBA-15 amount, solution pH, elution solvent, and the sorbent type, were investigated in detail. Under the optimum condition, the instrumental detection and quantitation limits calculated were less than 4.26 and 14.29ngmL(-1), respectively. The recoveries obtained for all the analytes were ranging from 89.22% to 103.46%. The experimental results suggested that SBA-15 was a promising material for the purification and enrichment of target flavanones from complex citrus fruit samples.

Efficient and recyclable heterogeneous zinc alkyl carboxylate catalyst for the synthesis of N-phenyl carbamate from aniline and dimethylcarbonate

A heterogeneous salt catalyst with zinc alkyl carboxylate chemically bonded on silica was highly active and recyclable in the synthesis of MPC.

Preparation of 4A-zeolite-based Ag nanoparticle composite catalyst and research of the catalytic properties

4A-zeolite base silver nanoparticles (Ag NPs) composite catalyst was prepared and the catalytic properties were researched.

Dual catalysis with magnetic chitosan: direct synthesis of cyclic carbonates from olefins with carbon dioxide using isobutyraldehyde as the sacrificial reductant

Magnetic chitosan was further functionalized with (ii) acetylacetonate complex [Co(acac)₂] and quaternary triphenylphosphonium bromide by targeting the –NH₂ and –OH moieties located on the surface of chitosan.

Cobalt-based metal organic framework as precursor to achieve superior catalytic activity for aerobic epoxidation of styrene

Novel nitrogen–cobalt catalysts are successfully prepared, and they exhibit high activity and stability in aerobic epoxidation of styrene without any initiator.

Epoxidation of styrene over Fe(Cr)-MIL-101 metal–organic frameworks

Fe(Cr)-MIL-101 metal–organic frameworks as efficient heterogeneous catalysts for the selective oxidation of styrene.

Spherical V-MCM-48: the synthesis, characterization and catalytic performance in styrene oxidation

High-quality spherical V-MCM-48 catalysts were successfully synthesized and showed higher catalytic activity for the selective oxidation of styrene to benzaldehyde.