Reaction-Controlled Phase-Transfer Catalysis for Propylene Epoxidation to Propylene Oxide

Ag-Based nanocomposites: synthesis and applications in catalysis

Ag-Based nanocomposites, including supported Ag nanocomposites and bimetallic Ag nanocomposites, have been intensively investigated as highly efficient catalysts because of their high activity and stability, easy preparation, low cost, and low toxicity. Herein, we systematically summarize and comprehensively evaluate versatile synthetic strategies for the preparation of Ag-based nanocomposites, and outline their recent advances in catalytic oxidation, catalytic reduction, photocatalysis and electrocatalysis. In addition, the challenges and prospects related to Ag-based nanocomposites for various catalytic applications are also discussed. In light of the most recent advances in Ag-based nanocomposites for catalysis applications, this review provides a comprehensive assessment on the material selection, synthesis and catalytic characteristics of these catalysts, which offers a strategic guide to build a close connection between Ag nanocomposites and catalysis applications.

Epoxidation of Alkenes by Hydrogen Peroxide over 12-Heteropolyacids of Molybdenum and Tungsten (H3PMo3W9O40) Combined with Cetylpyridinium Bromide

In the epoxidation of 4-vinylcyclohex-1-ene with H2O2 in monophasic acetonitrile solution catalysed by Keggin-type 12-heteropolyacids, i.e., H3PMo12- nW nO40 ( n = 0–12), which are precursors of active peroxo complexes, and phase transfer catalysts Q+Br–, the catalyst H3PMo3W9O40 showed the highest activity, giving a conversion of 98% and a selectivity of 88%. By this method, a variety of water-insoluble unactivated alkenes, internal or terminal, open chain or cyclic and isolated, were epoxidised under mild conditions and after relatively short reaction times. The state of the H3PMo3W9O40/CPB/H2O2/CH3CN system was studied using UV, IR, and 31P NMR spectroscopies with the [H2O2]: [HPA] ratio = 50. Several peroxo species were observed by 31P NMR spectroscopy at a lower field than the original heteropolyacids. Their composition varied regularly with that of the starting catalyst. The P-containing peroxo species formed were deduced as [(PO4){Mo4– xW xO20}]3- ( x = 0-4), which are the true catalytically active species under the reaction conditions.

Computational study on epoxidation of propylene by dioxygen using the silanol-functionalized polyoxometalate-supported osmium oxide catalyst

The silanol-functionalized POM-supported single-site Os oxide catalyst has been theoretically considered for epoxidation of propylene in the presence of dioxygen based on density functional theory calculations.

Homogeneous oxidative desulfurization catalyzed by a recoverable reaction-controlled phase transfer catalyst based on trilacunary Keggin polyoxometalate

A phosphotungstic reaction-controlled phase transfer catalyst was prepared and applied for the homogeneous oxidative desulfurization. Excellent desulfurization efficiency was achieved at 60 °C and the catalyst can be easily separated and recycled with ideal results.

Investigation on converting 1-butene and ethylene into propene via metathesis reaction over W-based catalysts

Supported W catalysts were extensively investigated for the conversion of 1-butene and ethylene into propene by metathesis reaction. The performance of catalysts was compared by using unsupported WO3, pure SBA-15, supported W/SBA-15 with different W loadings, varied calcination temperatures, and by changing the pretreatment gas atmosphere. The above catalytic results could be employed to deduce the reaction mechanism combined with characterization techniques such as BET, XRD, UV-vis DRS, Raman, pyridine-IR, XPS, and H2-TPR. In this study, over the investigated W/SBA-15 catalysts, the results showed that the silanol group (Si-OH) in SBA-15 could act as a weak Brønsted acid site for 1-butene isomerization. However, the metathesis reaction was catalyzed by W-carbene species. The initially formed W-carbenes (W[double bond, length as m-dash]CH-CH3) as active sites were derived from the partially reduced isolated tetrahedral WO x species which contained W[double bond, length as m-dash]O or W-OH bonds in W5+ species as corresponding Lewis or Brønsted acid sites. Furthermore, the W/SBA-15 being pretreated by H2O led to a complete loss of the metathesis activity. This was mainly due to the sintering of isolated WO x species to form an inactive crystalline WO3 phase as demonstrated by XRD patterns. On the other hand, the reduction of WO x species remarkably suppressed by H2O pretreatment was also responsible for the metathesis deactivation. This study provides molecular level mechanisms for the several steps involved in the propene production, including 1-butene isomerization, W-carbene formation, and metathesis reaction.

A computational study of the catalytic aerobic epoxidation of propylene over the coordinatively unsaturated metal–organic framework Fe3(btc)2: formation of propylene oxide and competing reactions

The aerobic epoxidation of propylene over the metal–organic framework Fe₃(btc)₂ (btc = 1,3,5-benzentricarboxylate) as catalyst has been investigated by means of density functional calculations.

Visible-light driven catalase-like activity of blackberry-shaped {Mo72Fe30} nanovesicles: combined kinetic and mechanistic studies

Catalase-like activity of blackberry-shaped {Mo₇₂Fe₃₀} nanovesicles was exploited in aqueous solution under visible-light irradiation.

Green catalysis for the selective oxidation of sulfides with high turnover numbers in water at room temperature

A hybrid catalyst based on monoprotonated divanadium-substituted phosphotungstate ([γ-HPV₂W₁₀O₄₀]⁴⁻) was synthesized and used for the selective oxidation of sulfides.

Selective catalytic dehydration of furfuryl alcohol to 2, 2'-difurfuryl ether using a polyoxometalate catalyst

The spice flavour compound 2, 2'-difurfuryl ether (DFE) is widely utilised in the food industry as it has a coffee-like, nutty, earthy, mushroom-like odour. However, despite intensive research efforts, to date, an environmentally friendly and practical synthetic preparation technique for 2, 2'-difurfuryl ether is still unavailable. Here, we investigate a new approach using polyoxometalate catalysts to selectively catalytically dehydrate furfuryl alcohol to 2, 2'-difurfuryl ether. We have successfully applied this methodology using the polyoxometalate (POMs) catalyst {[(CH3CH2CH2CH2)4N]2[SMo12O40]} to produce 2,2'-difurfuryl ether in a 30.86% isolated yield.

Synthesis, characterization and catalytic epoxidation properties of lanthanide-stabilized peroxoisopolytungstates

A series of new lanthanide-containing peroxoisopolyoxotungstates, K₆Na₄[H₃₂{Ln₄(WO₄)(H₂O)₁₆[W₇O₂₂(O₂)₂]₄}₃]·105H₂O [Ln = Ce^III(1), Nd^III(2), Sm^III(3), Tb^III(4), Er^III(5)], have been successfully synthesized and structurally characterized.

Synthesis of different structured FePO4 for the enhanced conversion of methyl cellulose to 5-hydroxymethylfurfural

Catalytic mechanism of FePO₄ for the conversion of methyl cellulose into 5-HMF.

MoOx–pyridine organic–inorganic hybrid wires as a reusable and highly selective catalyst for the oxidation of alcohols: a comparison study between reaction-controlled phase-transfer catalysis and heterogeneous catalysis

The different catalytic behaviors of Mo₃O₁₀(C₅H₆N)₂·H₂O wires (MoO_x–pyridine) in the selective oxidation of alcohols by means of molecular oxygen (O₂) and hydrogen peroxide (H₂O₂) as green oxidants were investigated.

A pH-controlled recyclable indolinooxazolidine tagged N-heterocyclic carbene Ru catalyst for olefin metathesis

A pH-controlled recyclable indolinooxazolidine tagged N-heterocyclic carbene Ru catalyst for olefin metathesis has been developed.

Applications of Liquid/Liquid Biphasic Oxidations by Hydrogen Peroxide with Ionic Liquids or Deep Eutectic Solvents

This Minireview focuses on recent applications of ionic liquids (ILs) and deep eutectic solvents (DESs) in biphasic oxidations in which the oxidizing agent corresponds to hydrogen peroxide. Biphasic reactions are accomplished when the substrate presents low or moderate solubility in aqueous (polar) systems and/or when separation of products and byproduct is an issue. The properties of the IL and DES allows the reaction activity to be intensified. On the other hand, the high chemical stability of the ionic solvents allows the use of hydrogen peroxide to minimize solvent degradation and unwanted byproducts. The experimental evidence presented herein shows that ILs and DESs can be used as cocatalysts, catalysts, and solvents to achieve enhanced yields and conversions. The process advantages, in terms of a reduction of volatile solvents, improve the safety and use of the oxidizing agent, which implies the possibility of developing new process improvements in the future.

Trinuclear nickel and cobalt complexes containing unsymmetrical tripodal tetradentate ligands: syntheses, structural, magnetic, and catalytic properties

The coordination chemistries of the tetradentate N2O2-type ligands N-(2-pyridylmethyl)iminodiethanol (H2pmide) and N-(2-pyridylmethyl)iminodiisopropanol (H2pmidip) have been investigated with nickel(ii) and cobalt(ii/iii) ions. Three novel complexes prepared and characterized are [(Hpmide)2Ni3(CH3COO)4] (1), [(Hpmide)2Co3(CH3COO)4] (2), and [(pmidip)2Co3(CH3COO)4] (3). In 1 and 2, two terminal nickel(ii)/cobalt(ii) units are coordinated to one Hpmide(-) and two CH3CO2(-). The terminal units are each connected to a central nickel(ii)/cobalt(ii) cation through one oxygen atom of Hpmide(-) and two oxygen atoms of acetate ions, giving rise to nickel(ii) and cobalt(ii) trinuclear complexes, respectively. Trinuclear complexes 1 and 2 are isomorphous. In 3, two terminal cobalt(iii) units are coordinated to pmidip(2-) and two CH3CO2(-). The terminal units are each linked to a central cobalt(ii) cation through two oxygen atoms of pmidip(2-) and one oxygen atom of a bidentate acetate ion, resulting in a linear trinuclear mixed-valence cobalt complex. 1 shows a weak ferromagnetic interaction with the ethoxo and acetato groups between the nickel(ii) ions (g = 2.24, J = 2.35 cm(-1)). However, 2 indicates a weak antiferromagnetic coupling with the ethoxo and acetato groups between the cobalt(ii) ions (g = 2.37, J = -0.5 cm(-1)). Additionally, 3 behaves as a paramagnetic cobalt(ii) monomer, due to the diamagnetic cobalt(iii) ions in the terminal units (g = 2.53, |D| = 36.0 cm(-1)). No catalytic activity was observed in 1. However, 2 and 3 showed significant catalytic activities toward various olefins with modest to good yields. 3 was slightly less efficient toward olefin epoxidation reaction than 2. Also 2 was used for terminal olefin oxidation reaction and was oxidised to the corresponding epoxides in moderate yields (34-75%) with conversions ranging from 47-100%. The cobalt complexes 2 and 3 promoted the O-O bond cleavage to ∼75% heterolysis and ∼25% homolysis.

One-pot synthesis of (-)-Ambrox

(−)-Ambrox is recognised as the prototype of all ambergris odorants. Widely used in perfumery, (−)-Ambrox is an important ingredient due to its unique scent and excellent fixative function. An environmentally friendly and practical preparation of (−)-Ambrox is still unavailable at present although a lot of attention has been paid to this hot research topic for many years. A one-pot synthesis of (−)-Ambrox was studied starting from (−)-sclareol through oxidation with hydrogen peroxide in the presence of a quaternary ammonium phosphomolybdate catalyst {[C₅H₅NC₁₆H₃₃] [H₂PMo₁₂O₄₀]}, which gave the product a 20% overall yield.

A discrete {Co4(μ3-OH)4}(4+) cluster with an oxygen-rich coordination environment as a catalyst for the epoxidation of various olefins

Using the sterically hindered terphenyl-based carboxylate, the tetrameric Co(ii) complex [Co4(μ3-OH)4(μ-O2CAr(4F-Ph))2(μ-OTf)2(Py)4] () with an asymmetric cubane-type core has been synthesized and fully characterized by X-ray diffraction, UV-vis spectroscopy, and electron paramagnetic resonance spectroscopy. Interestingly, the cubane-type cobalt cluster with 3-chloroperoxybenzoic acid as the oxidant was found to be very effective in the epoxidation of a variety of olefins, including terminal olefins which are more challenging targeting substrates. Moreover, this catalytic system showed a fast reaction rate and high epoxide yields under mild conditions. Based on product analysis and Hammett studies, the use of peroxyphenylacetic acid as a mechanistic probe, H2(18)O-exchange experiments, and EPR studies, it has been proposed that multiple reactive cobalt-oxo species Co(V)[double bond, length as m-dash]O and Co(IV)[double bond, length as m-dash]O were involved in the olefin epoxidation.