Selective Oxidation Of Styrene Research Articles

Solvent Free, Selective Oxidation of Styrene Catalyzed by Cobalt Acylpyrazolone Supported onto Neutral Alumina: Synthesis and Spectral Characterization

AbstractThe present work describes the synthesis of the Cobalt acylpyrazolone complex supported over neutral alumina and its use as a heterogeneous catalyst for selective oxidation of styrene. The catalyst mentioned here was characterized by various physicochemical techniques such as FT‐IR, TGA, CV, SCXRD, PXRD and BET. This heterogeneous catalyst has successfully been used to oxidize styrene to benzaldehyde in a solvent‐free condition with good conversion (87 %) and high selectivity (90 %) using H2O2 and TBHP as oxidants. The effects of the reaction parameters (catalyst concentration, reaction duration, and temperature) have also been investigated. The existing complex was discovered to be recyclable and sustainable with no change in conversion or selectivity for benzaldehyde. FT‐IR spectra of the regenerated catalyst indicated that the catalyst was undegraded and stable after the reaction. The novel feature of the current work reported in this paper is the selective oxidation of styrene without the need for solvents under mild conditions. Single Crystal Analysis.

Enhanced Catalytic Activity of a Copper(II) Metal-Organic Framework Constructed via Semireversible Single-Crystal-to-Single-Crystal Dehydration.

Herein, we present a copper(II) metal-organic framework, [Cu2(btec)(OH2)4]·2H2O (1) [(btec)4- = 1,2,4,5-benzenetetracarboxylate], that undergoes single-crystal-to-single-crystal transformations into two anhydrous phases 2' and 2″ with the chemical formula [Cu2(btec)], triggered by two-step dehydration at 403 and 433 K, respectively. After immersion in water for 3 days at room temperature, 2' transformed into [Cu2(btec)(OH2)] (3), while both 2' and 2″ took 1 week to revert to 1. Dynamic vapor sorption studies validated water-induced reversible structural transformations at 70% relative humidity (RH). According to single-crystal X-ray diffraction (SC-XRD), the local coordination geometry of the Cu2+ ion in 2' changed from a saturated octahedron to a coordinatively unsaturated square-based pyramid in 3, manifested by changes in color and dimensionality. From a topological point of view, all of the scaffolds show a binodal (3,6)-connected kgd topology with the point symbol {43}2{46}. In addition, the materials were thoroughly characterized using routine spectroscopic data and various analytical techniques. The catalytic activity of the microporous materials in the liquid-phase oxidation of styrene in acetonitrile, using 30% (wt) H2O2 as the oxidant, was investigated. The excellent performance of the monohydrous phase 3 was shown to be superior to the pristine framework and the anhydrous counterparts, as evidenced by a good turnover number (TON) and turnover frequency (TOF) = 82.6 and 21.0 h-1, respectively. Within 4 h, the substrates were catalytically oxidized to the desired products with up to 67% conversion and 100% benzaldehyde selectivity. It is worth noting that the accessible active metal sites and higher surface area enhanced the catalytic properties of 3. Furthermore, the maintenance of catalytic efficiency over five cycles and reusability are illustrated and discussed in terms of the structural differences of the microporous frameworks. Thus, a preliminary reaction mechanism for the selective oxidation of styrene is proposed. This study not only provides a fascinating example of MOF chromism achieved by thermal activation and rehydration but also sheds some light on the relationship between pore-surface- or metal-engineered sites in MOFs and their heterogeneous catalytic performances.

A Hierarchical Metal-Organic Framework Composite Aerogel Catalyst Containing Integrated Acid, Base, and Metal Sites for the One-Pot Catalytic Synthesis of Cyclic Carbonates.

Catalysis has played a decisive role in the development of unique chemical reactions to produce important chemicals. However, conventional stepwise synthetic routes that rely on individual catalysts to promote each step often suffer from ponderous processes for the isolation of intermediates that result in massive material losses and large economic expenditures. In addition, traditional powder forms of these catalysts suffer from poor processability and recoverability. Herein, we designed and prepared a hierarchical metal-organic framework (MOF) composite monolithic catalyst IL-Au@UiO-66-NH2/CMC that contains integrated acid (Zr4+), base (ionic liquid (IL)), and metal sites (Au nanoparticles (NPs)) to promote the one-pot preparation of cyclic carbonates from styrene derivatives and CO2. Highly dispersed Au NPs, IL 1-aminoethyl-3-methylimidazolium bromide ([C2NH2 MIM] [Br]), and MOF-positioned Lewis acid sites within this composite aerogel are separately responsible for catalyzing selective epoxidation of the styrene derivatives and the subsequent cycloaddition reaction of CO2 with intermediate styrene oxides. Importantly, inclusion of the imidazolium-based IL effectively modulates the size and chemical microenvironment of the Au NPs via electrostatic protection, leading to catalyst stability and its selective oxidation of styrene. Benefiting from the rapid mass transfer and high exposure of active sites within the pore-rich hierarchical nanostructure, IL-Au@UiO-66-NH2/CMC promotes high conversion (90.5%) of the styrene and selectivity (80.5%) for styrene carbonate (SC) formation in the one-pot process, a performance level that far exceeds those of related catalysts containing only Au NPs or IL (the selectivity of SC < 42%). Furthermore, the composite aerogel catalyst can be readily separated and recycled at least five times without a remarkable loss of activity and selectivity. The controllable integration of various active components in the hierarchical MOF composite aerogel herein should serve as the foundation for the design of multifunctional monolithic catalysts for other valuable tandem processes.

Enhanced photoelectric performance of ZnFe2O4 catalysts for oxidative carboxylation of styrene by tuning crystal planes and thermal and electrical conductivity

The photocatalytic oxidative carboxylation to yield cyclic carbonates was a promising approach for value-added utilization of olefins. Herein, various ZnFe2O4 (ZFO) based catalysts with different morphologies and supports were successfully prepared. Layered ZFO exposed highly active (422) crystal planes, which endowed the catalyst with narrow band gap and favorable electron transfer and charge separation, thereby promoting photocatalytic styrene epoxidation. Consequently, a 95 % selectivity for styrene oxide along with the complete conversion of styrene was achieved. Graphene with excellent electrical and thermal conductivity was compounded into ZFO based catalysts. On the one hand, ZFO/Graphene hybrids composed of 50 wt% graphene promoted fast charge transport in oxygen evolution reaction (OER), and the OER performance was comparable to the commercial RuO2 electrocatalyst. On the other, it exhibited significant photothermal effect and used into CO2 cycloaddition, delivering 95 % selectivity for styrene carbonate at a styrene oxide conversion of 95 %. As a result, a coupled photo-electro-heterogeneous catalytic system was proposed to yield styrene carbonate over ZFO based catalysts, including OER, styrene epoxidation and CO2 cycloaddition. This study provided an effective avenue for designing and fabricating ZFO based catalysts by crystal plane and support control.

Development of novel heterogeneous cobalt acylpyrazolone catalyst: Synthesis, characterization and selective oxidation of styrene to benzaldehyde

Cobalt acylpyrazolone complex was prepared and characterized using various spectral methods, FT-IR, TGA, UV–visible, DRS, magnetic study, and single crystal XRD. A heterogeneous catalyst consisting of neutral alumina and cobalt complex was synthesized and characterized using various physicochemical methods and successfully applied to styrene oxidation without a solvent. The effects of the reaction variables (mole proportion of the reactantto hydrogen peroxide and TBHP, quantity of the catalyst, reaction period and reaction temperature) were investigated. No appreciable catalytic activity reduction occurred when the catalyst was utilised again. The catalyst's recycling is verified by infrared and diffuse reflectance spectra confirming that the catalyst was intact and notdestroyed following the process. The work's unique feature is its benzaldehyde selectivity under benign reaction circumstances.

Efficient photocatalytic CO2 reduction coupled with selective styrene oxidation over a modified g-C3N4/BiOBr composite with high atom economy

A modified g-C3N4/BiOBr composite is developed for photocatalytic CO2 reduction to CO coupled with selective styrene oxidation.

Corrigendum: Size‐controlled Cobalt Ferrite Nanocrystals: Magnetically separable Reusable Nanocatalysts for Selective Oxidation of Styrene

Corrigendum: Size‐controlled Cobalt Ferrite Nanocrystals: Magnetically separable Reusable Nanocatalysts for Selective Oxidation of Styrene

Highly selective oxidation of styrene into benzaldehyde over nano CeWOx composite confined in N-doped carbon under solvent-free conditions

Highly selective oxidation of styrene into benzaldehyde with molecular oxygen under solvent-free conditions still remains a great challenge. Herein, Ce-modified heteropolyacid-based poly(ionic liquid)s were prepared as precursors followed by carbonization to obtain nano CeWOx composite confined in N-doped carbon (CeWOx@NC). Then, the as-prepared catalysts were further characterized by FT-IR, TG, XRD, XPS, BET, SEM, TEM-EDS and H2-TPR to discuss the relationship between the structure and performance. The nano CeWOx composite with a mixed valence state of W4+ and W6+ was formed and well dispersed in the N-doped carbon. Moreover, the valence ratio of W4+ to W6+, redox capacity and oxygen vacancies could be tailored by carbonization temperature and incorporation of Ce, which was strongly correlated with the catalytic performance of CeWOx@NC catalysts. Benefited from that, the CeWOx@NC800 catalyst displays outstanding catalytic performance for solvent-free oxidation of styrene into benzaldehyde with styrene conversion of 45.1%, benzaldehyde selectivity of 89.2% and TOF of 310.1 h−1 at the optimum reaction conditions. Furthermore, the catalyst has shown robust stability and reusability.

Fabrication of CuTNPc/MWCNTs composites by in-situ solvothermal method for efficient selective oxidation of styrene

The tetranitro-copper phthalocyanine/multi-walled carbon nanotubes (CuTNPc/MWCNTs) composites have been successfully fabricated by a straightforward in-situ solvothermal approach. The as-prepared CuTNPc/MWCNTs composites can be used as effective catalysts for the styrene catalytic oxidation to benzaldehyde. Effects of solvent type, oxidant type, catalyst dose, and reaction temperature on catalytic performance are investigated. It can be found that the CuTNPc/MWCNTs composites showed significant catalytic oxidation of styrene activity. Under the optimal conditions of 0.3 g styrene, 20 mg CuTNPc/MWCNTs, 3 mL TBHP as oxidant, and 5 mL THF at 90 ℃ for 6 h, the styrene conversion, and benzaldehyde selectivity could reach 99.74% and 79.53%, respectively. In addition, the possible reaction mechanism of styrene selective oxidation to benzaldehyde by CuTNPc/MWCNTs is also proposed.

Encapsulation of Microperoxidase‐8 into MIL‐101(Cr/Fe) Nanoparticles: A New Biocatalyst for the Epoxidation of Styrene

AbstractA new biocatalyst MP8@MIL‐101(Cr/Fe) was prepared by immobilization of a heme octapeptide, Microperoxidase 8 (MP8) within a mixed metal MOF, MIL‐101(Cr/Fe). Both MIL‐101(Cr/Fe) and MP8@MIL‐101(Cr/Fe) were characterized by PXRD, FTIR spectroscopy and TGA. The catalytic activity of MP8@MIL‐101(Cr/Fe) for the oxidation of styrene by H2O2 and tBuOOH was then examined under various reaction conditions (nature of the co‐solvent and of the oxidant, concentration of the oxidant and of the substrate, time, pH) and compared to that of MP8 alone. Under the best conditions used, MP8@MIL‐101(Cr/Fe) was then shown to catalyze the oxidation of styrene about 3 times more efficiently than MP8 alone with approximately 50 % selectivity for styrene oxide.

Modulating Charges of Dual Sites in Multivariate Metal-Organic Frameworks for Boosting Selective Aerobic Epoxidation of Alkenes.

Selective aerobic epoxidation of alkenes without any additives is of great industrial importance but still challenging because the competitive side reactions including C═C bond cleavage and isomerization are difficult to avoid. Here, we show fabricating Cu(I) single sites in pristine multivariate metal-organic frameworks (known as CuCo-MOF-74) via partial reduction of Cu(II) to Cu(I) ions during solvothermal reaction. Impressively, CuCo-MOF-74 is characteristic with single Cu(I), Cu(II), and Co(II) sites, and they exhibit the substantially enhanced selectivity of styrene oxide up to 87.6% using air as an oxidant at almost complete conversion of styrene, ∼25.8% selectivity increased over Co-MOF-74, as well as good catalytic stability. Contrast experiments and theoretical calculation indicate that Cu(I) sites contribute to the substantially enhanced selectivity of epoxides catalyzed by Co(II) sites. The adsorption of two O2 molecules on dual Co(II) and Cu(I) sites is favorable, and the projected density of state of the Co-3d orbital is closer to the Fermi level by modulating with Cu(I) sites for promoting the activation of O2 compared with dual-site Cu(II) and Co(II) and Co(II) and Co(II), thus contributing to the epoxidation of the C═C bond. When other kinds of alkenes are used as substrates, the excellent selectivity of various epoxides is also achieved over CuCo-MOF-74. We also prove the universality of fabricating Cu(I) sites in other MOF-74 with various divalent metal nodes.

Selective oxidation of vinylbenzenes &amp; acyloins in the presence of silver catalyst using molecular oxygen as terminal oxidant

Selective oxidation of styrene to benzaldehyde continues to be a quest for synthetic chemists. A number of transition metal based, metal free, nanocomposite-based catalysts have been developed for this transformation. We hereby report the oxidation of styrene into corresponding benzaldehydes using molecular oxygen as oxidant in the presence of catalytic amount of Ag2O. The reaction proceeded with a well-known oxidation of styrene-to-styrene oxide giving intermediates which lead to decarboxylative generation of aldehydes. One such intermediate was hydroxyketone. In view of the formation of hydroxyketone intermediate, we explored the oxidative dehomologation of α-hydroxy ketone via decarboxylation of 2-oxo-2-phenylacetic acid into benzoic acid using the same strategy. Both the reactions exhibited high functional group tolerance and a broad substrate scope.

Back Cover: Visible‐Light‐Promoted Switchable Selective Oxidations of Styrene Over Covalent Triazine Frameworks in Water (Angew. Chem. Int. Ed. 15/2023)

Covalent triazine frameworks were designed as metal-free and recyclable photocatalysts for visible-light-driven switchable selective oxidation of styrene into benzaldehyde or styrene oxide. As reported by Kai A. I. Zhang and co-workers in their Research Article (e202216159), the product formation selectivity was achieved by activation or deactivation of the specific photogenerated oxygen species in pure water.

Rücktitelbild: Mit sichtbarem Licht geförderte schaltbare selektive Oxidationen von Styrol über kovalente Triazin‐Gerüste in Wasser (Angew. Chem. 15/2023)

Covalent triazine frameworks were designed as metal-free and recyclable photocatalysts for visible light-driven switchable selective styrene oxidation into benzaldehyde or styrene oxide. As reported by Kai A. I. Zhang et al. in their Research Article (DOI: 10.1002/ange.202216159), the product formation selectivity was achieved by activation or deactivation of the specific photogenerated oxygen species in pure water.

Selective Styrene Oxidation Catalyzed by Phosphate Modified Mesoporous Titanium Silicate

Selective oxidation of organics over an efficient heterogeneous catalyst under mild liquid phase conditions is a very demanding chemical reaction. Herein, we first report the modification of the surface of mesoporous silica MCM-41 material by phosphate for the efficient incorporation of Ti(IV) in the silica framework to obtain highly ordered 2D hexagonal mesoporous material STP-1. STP-1 has been synthesized by using tetraethyl orthosilicate, triethyl phosphate, and titanium isopropoxide as Si, P, and Ti precursors, respectively, in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) under hydrothermal conditions. The observed specific surface area and pore volume of STP-1 were 878 m2g−1 and 0.75 ccg−1, respectively. Mesoporous STP-1 has been thoroughly characterized by XRD, FT-IR, Raman spectroscopy, SEM, and TEM analyses. Titanium incorporation (Ti/Si = 0.006) was confirmed from the EDX analysis. This mesoporous STP-1 was used as a heterogeneous catalyst for the selective oxidation of styrene into benzaldehye in the presence of dilute aqueous H2O2 as an oxidizing agent. Various reaction parameters such as the reaction time, the reaction temperature, and the styrene/H2O2 molar ratio were systematically studied in this article. Under optimized reaction conditions, the selectivity of benzaldehyde could reach up to 93.8% from styrene over STP-1. Further, the importance of both titanium and phosphate in the synthesis of STP-1 for selective styrene oxidation was examined by comparing the catalytic result with only a phosphate-modified mesoporous silica material, and it suggests that both titanium and phosphate synergistically play an important role in the high selectivity of benzaldehyde in the liquid phase oxidation of styrene.

Visible-Light-Promoted Switchable Selective Oxidations of Styrene Over Covalent Triazine Frameworks in Water.

Using photocatalytic oxidation to convert basic chemicals into high value compounds in environmentally benign reaction media is a current focus in catalytic research. The challenge lies in gaining controllability over product formation selectivity. We design covalent triazine frameworks as heterogeneous, metal-free, and recyclable photocatalysts for visible-light-driven switchable selective oxidation of styrene in pure water. Selectivity in product formation was achieved by activation or deactivation of the specific photogenerated oxygen species. Using the same photocatalyst, by deactivation of photogenerated H2 O2 , benzaldehyde was obtained with over 99 % conversion and over 99 % selectivity as a single product. The highly challenging and sensitive epoxidation of styrene was carried out by creating peroxymonocarbonate as an initial epoxidation agent in the presence of bicarbonate, which led to formation of styrene oxide with a selectivity up to 76 % with near quantitative conversion. This study demonstrates a preliminary yet interesting example for simple control over switchable product formation selectivity for challenging oxidation reactions of organic compounds in pure water.

Cumene Hydroperoxide-Induced Epoxidation of Styrene Using Cu2O and PbO as Catalysts

Styrene oxide (STOX), produced by epoxidation of styrene, is a pivotal building block in perfumery chemical and cosmeceutical industries. Catalytic performances of commercially available cuprous oxide (Cu2O) and lead oxide (PbO) are tested for epoxidation of styrene for selective production of styrene oxide (STOX). Cumene hydroperoxide (CHP) is used as the oxygen-inducing reagent in this study. Parametric study by altering the operating conditions indicates that lower temperature and lesser styrene in the feed aid styrene-based STOX selectivity, whereas there exists no significant effect of the catalyst loading on product selectivity. A maximum of ∼42.5% (∼45% STOX selectivity at ∼95% conversion of styrene) and ∼45% (∼50% STOX selectivity at ∼90% conversion of styrene) product yields have been recorded within 6 h of batch operation for Cu2O and PbO, respectively. Detailed deactivation study shows that the loss of catalyst activity upon reuse can be attributed to the combined effect of leaching of active sites and oxidation of the metal oxide catalyst on account of the oxidative nature of the reaction system. A suitable lumped kinetic model is proposed, which satisfactorily explains the trends in product yield and by/coproduct formation. Kinetic parameters are estimated by nonlinear regression along with a 95% confidence interval. The studies presented in this article can be considered useful for designing a technoeconomically feasible hydroperoxide-based route for the production of STOX as an alternative to the conventional chlorohydrin-based process.

Construction of Cu/MOF composites via controlling nucleation strategy with high catalytic activity

The composites, nanoparticles/metal-organic frameworks, are promising materials with unique physico-chemical property, which can not only adjust the properties of MOFs but also extend the application of MOFs. However, the preparation of nanoparticles/metal-organic frameworks is tedious and the catalytic activity of them is seriously affected. Herein, a rational strategy was proposed to fabricate new-type Cu nanoparticles (Cu0) supported HKUST-1(Cu) by controlling the nucleation process, where the Cu clusters were relatively active in the nucleation stage and reduced by methanol to transform into Cu nanoparticles with the aid of ultrasound and finally embedded into the framework structure of HKUST-1(Cu), which can effectively suppress the aggregation of Cu nanoparticles. Specially, Cu nanoparticles supported HKUST-1(Cu) was named as HKUST-1(Cu)-45. Compared with an 72.79% conversion and 70.89% selectivity for styrene oxide using HKUST-1(Cu) as the catalyst, the conversion and selectivity for styrene oxide using HKUST-1(Cu)-45 reached 90.94% and 73.21%, respectively. The results were mainly ascribed to the high surface area (1127 m2 g−1) and the exposed more catalytic active sites of HKUST-1(Cu)-45. Moreover, HKUST-1(Cu)-45 exhibited outstanding catalytic activity and structural stability. The insight may provide a significant inspiration for preparing various nanoparticles/metal-organic frameworks by adjusting the nucleation stage of MOFs.

Selective oxidation of styrene over nanostructured cerium–bismuth mixed oxide catalysts

The Ce0.7Bi0.3O2 catalyst exhibited superior catalytic activity in comparison to other cerium and bismuth based mixed oxides for styrene oxidation with 95% conversion and 85% selectivity to styrene epoxide.

Selective oxidation of styrene by H2O2 over novel supported palladium(ii)-based catalysts

The newly constructed bidentate ligand effectively inhibits the formation of palladium black. The bidentate ligand grafted on the solid support effectively promotes the redox cycle of the active component.