Catalytic performance of MnFeSi composite in selective oxidation of styrene, ethylbenzene and benzyl alcohol

Selective oxidation of styrene over transition metal-doped mesoporous silica catalyst

An inverse-micelle sol-gel method was used to prepare Ti and Fe-doped mesoporous silica catalysts, and they were utilized for selective oxidation of styrene to benzaldehyde. The amorphous peak of silica was confirmed by XRD and there were no peaks related to Ti or Fe oxides. Results indicate that the metals were homogeneously distributed in the silica matrix, leading to higher surface area and pore volume. Introduction of Ti species into mesoporous silica improved the total catalyst acidity and catalytic data revealed that the oxidation activity of Ti-doped mesoporous silica (Ti-MS) catalyst achieved 93% styrene conversion and 91% benzaldehyde selectivity under optimized conditions. Formic acid, phenylacetaldehyde, acetophenone and epoxy-styrene are all minor products of this reaction. The acid strength and the use of appropriate solvents and oxidants are crucial to achieving high styrene conversion and benzaldehyde yield. The catalysts were reusable up to 4 cycles without loss of activity.

Self-Assembled Bifunctional Copper Hydroxide/Gold-Ordered Nanoarray Composites for Fast, Sensitive, and Recyclable SERS Detection of Hazardous Benzene Vapors

Volatile organic compounds (VOCs), particularly monoaromatic hydrocarbon compounds (MACHs), pose a potential risk to the atmospheric environment and human health. Therefore, the progressive development of efficient detection methodologies is a pertinent need, which is still a challenge at present. In this study, we present a rapid and sensitive method to detect trace amounts of MACHs using a bifunctional SERS composite substrate. We prepared an Au/SiO₂ enhanced layer and a porous Cu(OH)₂ adsorption layer via microfluidic-assisted gas-liquid interface self-assembly. The composite substrate effectively monitored changes in benzaldehyde using time-varying SERS spectra, and track-specifically identified various VOCs such as benzene, xylene, styrene, and nitrobenzene. In general, the substrate exhibited a rapid response time of 20 s to gaseous benzaldehyde, with a minimum detection concentration of less than 500 ppt. Further experimental assessments revealed an optimum Cu(OH)₂ thickness of the surrounding adsorption layer of 150 nm, which can achieve an efficient SERS response to MACHs. Furthermore, the recoverable and reusable property of the composite substrate highlights its practicality. This study presents a straightforward and efficient approach for detecting trace gaseous VOCs using SERS, with significant implications in the designing of SERS substrates for detecting other VOCs.

Cr-Containing Rare-Earth Substituted Yttrium Iron Garnet Ferrites: Catalytic Properties in the Ethylbenzene Oxidation

A series of the Cr-containing erbium substituted yttrium iron garnet ferrites (ECYIG) was synthesized with distinct Cr amounts, herein referred to as Y3(Er0.02Fe5Cr1−x)O12, where x refers to Cr amounts from 0 to 0.05. The catalytic performance of the solids was investigated in ethylbenzene oxidation in the presence of hydrogen peroxide to assess the role of Cr and Er present in the YIG garnet lattice for fine chemistry compound production. Raman spectroscopy, HRTEM, EPR and FTIR revealed that the insertion of Er (at a fixed amount of 2%) in dodecahedral sites had a great impact on the catalytic activity of the garnets. Both Er3+ and Y3+ in the lattice simultaneously provided structural stability to the garnet structure in any harsh environment. XPS and EPR indicated that the Cr3+ ions replaced those of Fe3+ located in both octahedral and tetrahedral sites of the YIG garnets. The Cr3+ ions acted as electronic promoter to increase the oxidation rate of the Fe3+ active species responsible for activating the EB molecule. SEM-EDS demonstrated that the solids having Cr amounts lower than 4% experienced the most severe deactivation due to the Cr leaching and strong carbon species adsorption on the surface of the catalysts, which decreased their efficiency in the reaction.

Influence of the Metal Incorporation into Hydroxyapatites on the Deactivation Behavior of the Solids in the Esterification of Glycerol

The effects of the metal incorporation into hydroxyapatites on the deactivation behavior of the solids were examined in the esterification of glycerol (EG) reaction. The introduction of Cu, Co, or Ni ions by ion exchange in calcium-deficient hydroxyapatites resulted in active catalysts for the EG reaction. The metal contents were varied from 2.0 to 17.0%, providing better performances at rather high metal contents. Part of metal species existed in the hydroxyapatite lattice structure and also as isolated Cu2+, Ni2+, and Co2+ entities on the surface, as shown by XPS and EPR. The effects of the reaction temperature, reaction time, and glycerol to acetic acid molar ratios were deeply investigated. The spent solids used in this study were characterized by XRD, FTIR, SEM-EDS, chemical analyses, EPR, and XPS. The Cu2+–OH acid pairs could promote a superior catalytic performance of Cu-containing hydroxyapatites due to the resistance of these solids against leaching of the active species, which is even better than those of Co and Ni-containing counterparts with high metal contents. Cu into hydroxyapatite had a good reusability and long-term utilization for five consecutive cycles of 24 h under a glycerol to acetic acid molar ratio of 0.25 at 80 °C, and longer reaction times provide triacetin formation. This was due to the fact that Cu was stabilized by interacting with Ca, PO4, and OH sites into the hydroxyapatite lattice, being highly active for the EG reaction. The results also revealed that isolated Cu2+ sites played an important role in enhancing the glycerol conversion, intrinsically due to the Cu-containing hydroxyapatites ability to avoid strong adsorption of glycerol oligomers on the catalytic sites.

Fabrication, characterizations and performance of a high-efficiency micro-electrolysis filler for isobutyl xanthate (IBX) degradation

Micro-electrolysis is a cost-effective method widely applied in wastewater treatment. In this paper, a high-efficiency micro-electrolysis filler was prepared by a facile calcination method for the degradation of isobutyl xanthate (IBX). The optimization of filler fabrication process was investigated from aspects of compressive strength, abrasion loss and degradation rate. Combined with multi-characterization techniques, it can be found that the zero-valent iron (ZVI) was partially changed to Fe(2+) in the phase of fayalite (Fe₂SiO₄) during the treatment. The influence of operation parameters of filler dosage, initial pH and initial concentration were thoroughly studied. The result shows that the IBX degradation rate by optimized filler can reach 93.30%, superior to that of Fe/C filler (the element Fe kept at ZVI during heat treatment) with 61.8% removal. The degradation pathway of IBX was studied by GC-MS in details and the bis(2-methylpropyl)carbonate was postulated as the main by-product. The stability of filler was evaluated by batch cycle tests and column tests. This work provides a novel perspective about micro-electrolysis filler preparation. The extraordinary performance brings it potential for industrial application.

Preparation and characterization of a copper oxide nanoparticle-supported red-mud catalyst for liquid phase oxidation of ethyl benzene to acetophenone

In this study, liquid phase oxidation of ethyl benzene to acetophenone was widely investigated using a new recyclable supported catalyst of CuO nanoparticles impregnated over activated red-mud (CuO_AARM).

Fabricating Surface-Functionalized CsPbBr3/Cs4PbBr6 Nanosheets for Visible-Light Photocatalytic Oxidation of Styrene

The halide perovskite (PVSK) material, an excellent light absorber with fast carrier kinetics, has received increased attention as a potential photocatalyst for organic synthesis. Herein, we report a straightforward synthesis of chemically modified halide perovskite and its application as an efficient photocatalyst to convert styrene into benzaldehyde. A simple method is employed to synthesize the chemically modified CsPbBr₃/Cs₄PbBr₆ nanosheets by using ZrCl₄ to simultaneously achieve the Cl doping and the surface modification with Zr species. The photocatalytic oxidation rate of styrene to benzaldehyde catalyzed by surface-modified CsPbBr₃/Cs₄PbBr₆ nanosheets under visible light can reach 1,098 μmol g⁻¹ h⁻¹, 2.9 times higher than that of pristine CsPbBr₃/Cs₄PbBr₆ nanosheets (372 μmol g⁻¹ h⁻¹). The enhanced photocatalytic performance may originate from the modified band structure induced by the synergistic effect of Cl doping and surface modification, whereby the same methodology can be applied to MAPbBr₃. This work demonstrates the surface modification of PVSK materials and their potential as efficient photocatalyst toward organic synthesis.

Acid Red 66 Dye Removal from Aqueous Solution by Fe/C-based Composites: Adsorption, Kinetics and Thermodynamic Studies

The presence of synthetic dyes in water causes serious environmental issues owing to the low water quality, toxicity to environment and human carcinogenic effects. Adsorption has emerged as simple and environmental benign processes for wastewater treatment. This work reports the use of porous Fe-based composites as adsorbents for Acid Red 66 dye removal in an aqueous solution. The porous FeC and Fe/FeC solids were prepared by hydrothermal methods using iron sulfates and sucrose as precursors. The physicochemical properties of the solids were evaluated through X-ray diffraction (XRD), Scanning electron microscopy coupled with Energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared s (FTIR), Raman and Mössbauer spectroscopies, nitrogen adsorption–desorption isotherms, Electron Paramagnetic Resonance (EPR) and magnetic saturation techniques. Results indicated that the Fe species holds magnetic properties and formed well dispersed Fe₃O₄ nanoparticles on a carbon layer in FeC nanocomposite. Adding iron to the previous solid resulted in the formation of γ-Fe₂O₃ coating on the FeC type structure as in Fe/FeC composite. The highest dye adsorption capacity was 15.5 mg·g⁻¹ for FeC nanocomposite at 25 °C with the isotherms fitting well with the Langmuir model. The removal efficiency of 98.4% was obtained with a pristine Fe sample under similar experimental conditions.

Hierarchical hollow nickel silicate microflowers for selective oxidation of styrene

Developing heterogeneous non-precious metal catalysts that can achieve high catalytic activity and good product selectivity at the same time is still a challenging and interesting work for the selective oxidation of styrene into valuable chemicals from environmental and industrial points of view. Herein, hierarchical hollow nickel silicate (Ni₃Si₂O₅(OH)₄) microflowers assembled from well-defined Ni₃Si₂O₅(OH)₄ nanosheets have been prepared by a facile one-pot hydrothermal method. The intriguing structure endows the hollow Ni₃Si₂O₅(OH)₄ microflowers a high surface area of 177.4 m² g^-1 and an average pore size of 3.9 nm. When employed as a catalyst for the selective oxidation of styrene in the presence of hydrogen peroxide as a ecological sustainable green oxidant, the Ni₃Si₂O₅(OH)₄ exhibits an attractive catalytic performance with a remarkably high styrene conversion of 99.3% and a high selectivity of 81.1% to benzaldehyde.

Co/rGO synthesized via the alcohol-thermal method as a heterogeneous catalyst for the highly efficient oxidation of ethylbenzene with oxygen

Co₃O₄ nanoparticles uniformly dispersed on reduced graphene oxide (Co/rGO) were synthesized by the alcohol-thermal method as a highly efficient catalyst with initiator NHPI for the selective oxidation of ethylbenzene to acetophenone using O₂ as a green oxidant.

A 3D-honeycomb-like catalyst: a nitrogen-doped carbon material with cobalt and manganese-oxide for C–H bond oxidation

A three dimensional mesoporous honeycomb-like material that is multifunctional and easily recoverable, and shows efficient performance is described.

CeFe-Based Bead Nanocomposites as Catalysts for Oxidation of Ethylbenzene Reaction

Oxides with good catalytic performances and more selectivity to valuable chemicals attract numerous research interests for the oxidation of hydrocarbon fuels. Taking advantage of the nanocasting route, CeFe-based nanocomposites were prepared and characterized to achieve superior stability in the oxidation of cyclic compounds. Adding a third metal (Me = Ni2+, Mn2+/Mn3+ or Co2+/Co3+) to the CeFe-based oxide helped the formation of Ce3+/Ce4+, Fe2+/Fe3+ and active couples in the ternary nanocomposites. The solids having a spherical morphology and good textural properties enabled the formation of promising ternary oxide catalysts for the oxidation of ethylbenzene compared with those of binary and single monoxide nanocomposites. The close contact among the Ce3+/Ce4+ and Fe2+/Fe3+ pairs with Ni2+ species provided the formation of a highly stable CeFeNi catalyst with enhanced performance in the oxidation of cyclic compounds such as ethylbenzene, styrene and benzyl alcohol substrates.

Highly selective oxidation of styrene to benzaldehyde over a tailor-made cobalt oxide encapsulated zeolite catalyst

A tailor-made catalyst with cobalt oxide particles encapsulated into ZSM-5 zeolites (Co₃O₄@HZSM-5) was prepared via a hydrothermal method with the conventional impregnated Co₃O₄/SiO₂ catalyst as the precursor and Si source. Various characterization results show that the Co₃O₄@HZSM-5 catalyst has well-organized structure with Co₃O₄ particles compatibly encapsulated in the zeolite crystals. The Co₃O₄@HZSM-5 catalyst was employed as an efficient catalyst for the selective oxidation of styrene to benzaldehyde with hydrogen peroxide as a green and economic oxidant. The effect of various reaction conditions including reaction time, reaction temperature, different kinds of solvents, styrene/H₂O₂ molar ratio and catalyst dosage on the catalytic performance were systematically investigated. Under the optimized reaction condition, the yield of benzaldehyde can achieve 78.9% with 96.8% styrene conversion and 81.5% benzaldehyde selectivity. Such an excellent catalytic performance can be attributed to the synergistic effect between the confined reaction environment and the proper acidic property. In addition, the reaction mechanism with Co₃O₄@HZSM-5 as the catalyst for the selective oxidation of styrene to benzaldehyde was reasonably proposed.