Microwave-assisted synthesis of α-Fe2O3/ZnFe2O4/ZnO ternary hybrid nanostructures for photocatalytic applications

Solar-driven highly efficient photocatalytic decomposition of toxic organic contaminants using magnetically separable α-Fe₂O₃/ZnFe₂O₄/ZnO ternary hybrid nanodiscs is reported. α-Fe₂O₃/ZnFe₂O₄/ZnO ternary hybrid nanostructures were synthesized by microwave-assisted co-precipitation and simple co-precipitation methods and well characterized by XRD, micro-Raman, FESEM and UV–vis spectroscopy. FESEM micrographs revealed nanodiscs in case of microwave-assisted co-precipitation whereas nanoparticles and their aggregates were formed under co-precipitation combined with calcination. XRD and Raman studies confirmed the hybrid nature of prepared α-Fe₂O₃/ZnFe₂O₄/ZnO nanostructures. Photocatalytic performance of α-Fe₂O₃/ZnFe₂O₄/ZnO hybrid nanostructures was investigated by carrying out the photodegradation of organic dyes MB and MG under solar light illumination. The prepared α-Fe₂O₃/ZnFe₂O₄/ZnO ternary hybrid magnetic nanodiscs decomposed MB and MG dyes in only 32 and 24 min, respectively. α-Fe₂O₃/ZnFe₂O₄/ZnO hybrid nanodiscs showed excellent photocatalytic performance together with reusability and easy magnetic separation demonstrating its suitability for solar-driven photocatalytic water purification applications. In-situ scavenger studies showed ?OH radicals are the main active radicals in solar-driven photocatalysis by α-Fe₂O₃/ZnFe₂O₄/ZnO nanodiscs. The tentative mechanism of growth of α-Fe₂O₃/ZnFe₂O₄/ZnO ternary hybrid nanodiscs and the photocatalytic mechanism are discussed.     

Effect of Tourmaline Addition on the Catalytic Performance and SO2 Resistance of NixMn3−xO4 Catalyst for NH3-SCR Reaction at Low Temperature

Catalysis Letters - NixMn3?xO4 and NixMn3?xO4/T (T represents tourmaline) catalysts with a double-layer hollow structure were prepared by a rigid template method for low-temperature...     

A Novel KCaNi/α-Al2O3 Catalyst for CH4 Reforming with CO2

A potassium and calcium co-promoted nickel catalyst (KCaNi/-Al₂O₃) prepared by a direct impregnation method possessed a high activity, high stability and excellent coke resistance properties in CH₄ reforming with CO₂. XRD, XPS and H₂-TPR characterizations indicated that (i) Ca and K strengthened the interaction between Ni and -Al₂O₃ and promoted the formation of a unique NiAl₂O₄ phase on the surface of the catalyst and (ii) Ca and K increased the dispersion of Ni and retarded its sintering. Coking reactions (CH₄ temperature-programmed decomposition and O₂-TPO) disclosed that K reduced carbon formation via CH₄ decomposition.     

Synthesis and Characterization of Copper(II)–Cysteine/SiO2–Al2O3 as an Efficient and Reusable Heterogeneous Catalyst for the Oxidation of Aromatic Alcohols

In the present study, heterogeneous copper(II)–cysteine/SiO₂–Al₂O₃ catalyst was successfully prepared by a simple adsorption method. The physical and chemical properties of Cu(II)–cysteine/SiO₂–Al₂O₃ were investigated by X-ray diffraction, thermal gravimetric analyzer, FT–IR spectroscopy, Brunauer–Emmett–Teller, UV–Vis spectroscopy, scanning electron microscopy and atomic absorption spectrometer. The obtained composite was effectively employed as catalyst for selective oxidation of various aromatic alcohols to corresponding aldehydes in high yields using hydrogen peroxide as an oxidant under mild condition. The catalyst can be recycled over five times without significant loss of activity.     

ZnFe2O4@Polypyrrole nanocomposites as an efficient broadband electromagnetic wave absorber at 2–40 GHz

In this work, polypyrrole-coated ZnFe₂O₄ (ZnFe₂O₄@PPy) nanocomposites were successfully synthesized via a simple in-situ polymerization process, then evaluated as electromagnetic wave (EMW) absorbers over the 2–40 GHz frequency range. The ZnFe₂O₄@PPy nanocomposites exhibited excellent EMW absorption properties, including very low reflection losses (−42.31 dB at 30.24 GHz and a thickness of 2.5 mm) and a broad absorption bandwidth of 28.20 GHz (from 9.66 to 37.86 GHz). The EMW absorption properties of the ZnFe₂O₄@PPy nanocomposites could be adjusted by changing the PPy shell thickness and also the thickness of the absorber (1–2.5 mm). The excellent microwave absorption performance of the ZnFe₂O₄@PPy nanocomposites is attributable to the synergistic effects of magnetic losses (ZnFe₂O₄ nanoparticles), dielectric losses (ZnFe₂O₄ and PPy) and interfacial relaxation losses at ZnFe₂O₄-PPy interfaces.     

Ag2O–Al2O3–ZrO2 Trimetallic Nanocatalyst for High Performance Photodegradation of Nicosulfuron Herbicide

Topics in Catalysis - In the present study, Ag2O–Al2O3–ZrO2 based trimetallic oxide nanocatalyst was designed using simple microwave assisted reduction method. It was characterized...     

Palladium Nanoparticles Supported on Poly(2-hydroxyethyl methacrylate)/KIT-6 Composite as an Efficient and Reusable Catalyst for Suzuki–Miyaura Reaction in Water

Pd nanoparticle-poly(2-hydroxyethyl methacrylate)/KIT-6 (Pd-PHEMA/KIT-6) composite was fabricated through in situ polymerization method and was evaluated as a novel heterogeneous catalyst in Suzuki–Miyaura cross coupling reactions of aryl halides and phenylboronic acid in an aqueous medium. The catalyst was characterized by XRD, FT-IR, UV–Vis, TG, BET, and TEM techniques. The results revealed that the supported catalyst Pd-PHEMA/KIT-6 exhibited excellent catalytic activity for the coupling of aryl iodides, aryl bromides, and aryl chlorides. This heterogeneous catalyst could be reused at least nine times without any decrease in activity.     

High‐activity catalyst of SO 4 2− /ZrO2 supported on γ‐Al2O3 for n‐butane isomerization

A series of Al₂O₃supported SO ₄ ^2– /ZrO₂ superacid catalysts (named SZ/Al₂O₃) were prepared by a precipitation method and their catalytic behavior for nbutane isomerization at low temperature in the absence of H₂ and at high temperature in the presence of H₂ was studied in this paper. The catalytic activities of some of these catalysts were enhanced significantly at both low and high temperatures. At 250°C after 6 h on stream, the steady activity of the most active sample, 60%SZ/Al₂O₃, is about two times higher than that of conventional SZ. The texture properties of catalysts were studied by the methods of XRD and the adsorption of N₂. Experimental evidence of IR of adsorbed pyridine indicates that the significant activity enhancements of SZ/Al₂O₃ catalysts are caused by the increasing of the amount of strong acid sites.     

Preparation of magnetic α-Fe2O3/ZnFe2O4@Ti3C2 MXene with excellent photocatalytic performance

The high conductivity Ti₃C₂ MXene with the unique lamellar nanostructure can effectively improve photoelectrocatalytic ability of composite as cocatalyst. In this paper, the magnetic α-Fe₂O₃/ZnFe₂O₄ heterojunctions were obtained using one-step hydrothermal synthesis. And α-Fe₂O₃/ZnFe₂O₄@Ti₃C₂ MXene photocatalyst can be easily obtained by ultrasonic assisted self-assembly approach for dispersing magnetic α-Fe₂O₃/ZnFe₂O₄ heterojunctions on Ti₃C₂ MXene surface. Due to the improving photoelectron ability, the α-Fe₂O₃/ZnFe₂O₄@Ti₃C₂ MXene was found to exhibit the higher photocatalytic ability than the α-Fe₂O₃/ZnFe₂O₄ heterojunctions in eliminating Rhodamine B (RhB) pollutant and toxic Cr(Ⅵ) in water. Even more important, as a magnetic composite, the 10 wt% α-Fe₂O₃/ZnFe₂O₄@Ti₃C₂ MXene photocatalyst exhibited the excellent reusability. The terrific photocatalytic ability is due to the numerous heterostructure interfaces, the increase of visible light harvesting and high conductivity.     

New catalyst of SO 4 2− /Al2O3–ZrO2 for n-butane isomerization

The catalytic behavior of Al-promoted sulfated zirconia for n-butane isomerization at low temperature in the absence of H₂ and at high temperature in the presence of H₂ was studied. The addition of Al enhances the activity and stability of the catalysts for reaction at 250°C and in the presence of H₂ significantly. After on stream for 120 h, the n-butane conversion of the catalyst containing 3 mol% Al₂O₃ keeps steadily at 88% of its equilibrium conversion and no observable trend of further deactivation has been observed. The difference in behavior of the promoted and unpromoted catalysts at low and high temperature is associated with a change of reaction mechanism from bimolecular to monomolecular. Experimental evidence is presented to show that the promoting effect of Al is different from that of the transition metals. Microcalorimetric measurements of NH₃ adsorption on catalysts reveal that the remarkable activity and stability of the Al-promoted catalysts are caused by an enhancement in the number of acid sites effective for the isomerization reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

Rh–Sr/Al2O3 Catalyst for N2O Decomposition in the Presence of O2

The improving effect of Sr in the catalytic activity of Rh for N₂O decomposition has been studied under 1,000 ppm N₂O/He and 1,000 ppm N₂O/5% O₂/He (GHSV = 10,000 h^?1). Different techniques have been used for catalysts characterization: TEM, SEM-EDX, XRD, N₂ adsorption at ?196 °C and in situ XPS. Sr favours the Rh dispersion and reduction under reaction conditions, and allows the low temperature removal of N₂O in the presence of O₂ (100% decomposition at 350 °C).     

High Efficient Production of Hydrogen from Bio-oil Using Low-temperature Electrochemical Catalytic Reforming Approach Over NiCuZn–Al2O3 Catalyst

High-efficient production of hydrogen from bio-oil was performed by a novel electrochemical catalytic reforming method over the NiCuZn–Al₂O₃ catalyst. The influences of current on the hydrogen yield, carbon conversion and products’ distribution were investigated. Both the hydrogen yield and carbon conversion were remarkably enhanced by the current through the catalyst, reaching nearly complete conversion with a hydrogen yield of 93.5% even at low reforming temperature of 400 °C. The thermal electrons would play important roles in promoting the reforming reactions of the oxygenated-organic compounds in bio-oil, molecular dissociation and the catalyst reduction.     

Nanostructure composite ZnFe2O4–FeFe2O4–ZnO immobilized on glass: Photocatalytic activity for degradation of an azo textile dye F3B

An efficient and scalable one-pot synthetic method to prepare nanostructure composite of ZnFe₂O₄–FeFe₂O₄–ZnO (ZFZ) has been investigated. This method is based on thermal decomposition of iron(III) acetate and zinc acetate in monoethanolamine (MEA) as a capping agent. Moreover, thermogravimetric analysis (TG-DTG) was performed to determine the temperature at which the decomposition and oxidation of the chelating agents took place. ZFZ was immobilized on glass using doctor blade method and calcinated at different temperatures. The properties of the ZFZ nanocomposite have been examined by different techniques, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and diffuse reflectance (DRS). FESEM shows that nanocomposite is monocrystallines and a narrow dispersion in size of 48 nm. XRD confirms that the prepared nanocomposite is composed of franklinite, ZnFe₂O₄ (54%), magnetite, FeFe₂O₄ (8%) and wurtzite, ZnO (48%). Photocatalytic activity of ZFZ immobilized on glass was carried out by choosing an azo textile dye, Reactive Red 195 (F3B) as a model pollutant under UV irradiation with homemade photocatalytic apparatus and the results indicated that ZFZ exhibited good photocatalytic activity.     

Active Sites of a NiSO4/γ-Al2O3 Catalyst for the Oligomerization of Isobutene

Structural characterization, the mechanism of catalytic activity generation and the nature of active sites of a NiSO₄/γ-Al₂O₃ catalyst for isobutene oligomerization were studied by temperature programmed reduction (TPR), X-ray diffraction (XRD), diffuse reflectance infrared fourier transformed (DRIFTS) and X-ray photoelectron spectroscopy (XPS) techniques. The TPR measurements together with the XRD data indicated that calcination of the catalyst at 500 °C did not form either nickel oxide or nickel aluminate. The presence of only one type of surface nickel species formed by the incorporation of nickel ions into the surface vacant sites of γ-alumina lattice was indicated by XPS with Ar⁺ ions sputtering and TPR measurements. XPS analysis of the calcined catalyst suggested that the oxidation state of nickel ions in the calcined catalyst was (+2) and after calcination the nickel ions were coordinated to relatively more basic ligands. The surface acid centers of the catalyst were found to be only Lewis type. SO₄ ^2? ions were found to be present as a chelating bidentate ligand and enhanced the acidity of metal ( $ {\text{Al}}^{3 + } $ and/or $ {\text{Ni}}^{2 + } $ ) Lewis acid centers. The results suggested that the combined effects of the presence of the bidentate SO₄ ^2? ligand and dehydroxylation generate coordinatively unsaturated $ {\text{Ni}}^{2 + } $ that interact with isobutene during the oligomerization reaction. The formation of lower-valent nickel ions ( $ {\text{Ni}}^{x + } ,x\; \le\; 1 $ ) was demonstrated by in situ DRIFTS using CO as a probe molecule and by XPS measurements. Formation of a binuclear bridging carbonyl complex, $ [{\text{Ni}}({\text{CO}})^{ + } ]_{2} $ suggested that some lower-valent nickel species were formed via in situ reduction by isobutene. Analysis of Ni 2p photolines indicated the appearance of a new lower-valent nickel species ( $ {\text{Ni}}^{x + } ,x \;\le\; 1 $ ) during the course of isobutene oligomerization. Hence it is plausible that lower-valent nickel species might act as the active center for the oligomerization reaction, while the SO₄ ^2? ions enhance the acidity of the Lewis acid sites on the surface and assist in the adsorption of reactant molecules on the surface.