A comparative study of the catalytic nitration of toluene over bimetallic Ce-Mn modified Hβ zeolite

Bimetallic cerium-manganese modified Hβ zeolite sample (Ce/Mn-Hβ) was prepared by ultrasonic assisted impregnation method and applied in nitration of toluene. The characterization results show that the active components (Ce and Mn) are successfully introduced into the framework of Hβ zeolite. The catalyst shows excellent catalytic activity and reusability for the nitration of toluene, giving high para selectivity. Under optimized conditions, it gives 68.7% selectivity to para-nitrotoluene at 88.6% conversion over Ce/Mn-Hβ in the presence of acetic anhydride (Ac₂O). The theoretical calculations indicate that the Ce/Mn bimetallic active sites in modified Hβ zeolite can easily activate the nitrification reagent (AcONO₂), and the enhancement of para selectivity is owing to the steric hindrance of catalyst. Furthermore, the reaction mechanism was proposed by the combination of experimental results and theoretical calculations.     

Alkylation of toluene with 1‐dodecene over HFAU zeolite. Deactivation and regeneration

The alkylation of toluene with 1dodecene was carried out over a HFAU zeolite (total and framework Si/Al ratio = 25) under the following conditions: fixedbed reactor, 90°C, molar toluene/dodecene ratio of 3, WHSV =10 h^–. Monododecyltoluenes are selectively formed, bidodecyltoluenes appearing only in low amounts at a complete conversion of dodecene. Tridodecyltoluenes are also formed inside the supercages but cannot desorb from the zeolite. These compounds, mainly located in the outer part of the crystallites are responsible for catalyst deactivation. However, tridodecyltoluenes can be completely removed by treatment under toluene flow, which allows a complete regeneration of the catalyst. This removal occurs by transalkylation between tridodecyltoluenes and toluene molecules with a final formation of monododecyltoluenes. At least, the first transalkylation steps occur between toluene in the liquid phase and tridodecyltoluenes in the zeolite pores (pore mouth catalysis).     

Friedel–Crafts type benzylation and benzoylation of aromatic compounds over Hβ zeolite modified by oxides or chlorides of gallium and indium

Liquid phase benzylation (by benzyl chloride) and benzoylation (by benzoyl chloride) of benzene and other aromatic compounds over different Ga- and In-modified Hβ zeolite catalysts at 80 °C have been investigated. An impregnation of the zeolite by oxides or chlorides of Ga and In makes the zeolite highly active in the benzylation process but it results in a decrease in the acidity, particularly the strong acid sites (measured in terms of the ammonia chemisorbed at 250 °C) of the zeolite. Both the redox function, created due to the modification of the Hβ zeolite by Ga or In, and the zeolitic acidity seem to play important role in the benzylation or benzoylation process. Among the different Ga- and In-modified Hβ zeolite catalysts, the In₂O₃/Hβ showed highest activity for the benzene benzylation. This catalyst also showed high activity for both the benzylation and benzoylation of other aromatic compounds, even in the presence of moisture in the reaction mixture; in case of the benzoylation, the moisture has beneficial effect. The In₂O₃/Hβ catalyst can be reused in the benzylation for several times. Kinetics of benzene benzylation (using excess of benzene) over the different Ga- and In-modified Hβ zeolite catalysts has also been investigated. A plausible mechanism for the activation of both the reactants (aromatic substrate and benzyl or benzoyl chloride, forming corresponding carbocation) over the catalyst and also for the reaction between the carbocation and the activated and/or non-activated aromatic substrate is proposed.     

Esterification of levulinic acid to ethyl levulinate over bimodal micro–mesoporous H/BEA zeolite derivatives

A series of bimodal micro–mesoporous H/BEA zeolite derivatives were prepared by the post-synthesis modification of H/BEA zeolite by NaOH (0.05 M–1.2 M) treatment. Samples were characterized by powder XRD, low temperature nitrogen adsorption/desorption, temperature programmed desorption of ammonia and ICP. The mesopore formation was found to play a crucial role in liquid phase esterification of levulinic acid with ethanol. The enhanced catalytic activity of a bimodal micro–mesoporous H/BEA zeolite derivative (H/BEA_0.10) prepared by treatment with 0.1 M NaOH can be mainly attributed to the high mesoporosity coupled with better preserved crystallinity and acidic properties.     

Synthesis and luminescence of Y2O3:Eu inorganic–organic hybrid nanostructures with thenoyltrifluoroacetone

Cubic Y₂O₃:Eu³⁺ nanoparticles with a size about 32 nm were synthesized using a facile hydrothermal method followed by an annealing process. As expected, the Y₂O₃:Eu³⁺ nanoparticles had a broad Eu–O excitation band ranging from 200 nm to 285 nm peaking at about 260 nm. The Y₂O₃:Eu³⁺ nanoparticles were then used to fabricate the inorganic–organic hybrid nanostructures with thenoyltrifluoroacetone (TTA). The Y₂O₃:Eu³⁺–TTA hybrid nanostructures exhibited a new strong excitation band ranging from 280 nm to 390 nm peaking at about 368 nm. This new excitation band was attributed to the energy transfer mechanism of the Y₂O₃:Eu³⁺–TTA hybrid system. It is interesting to note that this energy transfer mechanism had a close interaction with the Eu–O excitation of Y₂O₃:Eu³⁺ nanoparticles. The phase structures, chemical bonding information, microstructural characteristics and luminescence properties were investigated.     

Reactivity of surface isocyanate species with NO, O2 and NO+O2 in selective reduction of NOχ over Ag/Al2O3 and Al2O3 catalysts

Reactivity of surface isocyanate (NCO(a)) species with NO, O₂ and NO+O₂ in selective reduction of NOχ over Ag/Al₂O₃ and Al₂O₃ catalysts was studied by a pulse reaction technique and an in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The NCO(a) species on Ag/Al₂O₃ reacted with O₂ or NO+O₂ mixture gas to produce N₂ effectively above 200°C, while the reaction of NCO(a) with NO hardly produced N₂ even at 350°C. In the case of Al₂O₃ alone, less N₂ was detected in the reaction of NCO(a) with NO+O₂, indicating that silver plays an important role in the N₂ formation from NCO(a). These behaviors of the reactivity of NCO(a) species with reactant gases were in good agreement with the changes in NCO(a) bands shown by in situ DRIFT measurements. Based on these findings, the role of NCO(a) species in the selective reduction of NOχ on Ag/Al₂O₃ and Al₂O₃ catalysts is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

A novel catalytic method for the alkylation of benzene to diphenylmethane over H‐ZSM‐5 zeolite catalysts

Vapour‐phase catalytic alkylation of benzene to diphenylmethane in high selectivity (92.5%) at 30.7 wt% conversion of benzene is reported for the first time using dichloromethane (DCM) as an alkylating agent and H‐ZSM‐5 as the catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Simultaneous control of particle size and morphology of α-CaSO4·1/2H2O with organic additives

Here we reported a method to simultaneously control the particle size and morphology of α-CaSO₄·1/2H₂O (α-HH) prepared from flue gas desulfurization gypsum by adjusting the succinic acid concentration and glycerol content under mild conditions. Succinic acid controlled the crystal morphology by adsorption onto α-HH surfaces, and glycerol controlled the crystal particle size, in which an increase in the maximal relative supersaturation (S_max) and nucleation rate of α-HH was hypothesized to cause the change in α-HH particle size. Then, based on the method, α-HH with different particle sizes but with almost the same morphology was prepared, and the influence of the crystal particle size on the mechanical strength of the α-HH pastes was explored. With decreasing α-HH particle size from about 26 to 5 μm, the dry compressive strength of the pastes made from the α-HH decreased remarkably from 68.02 to 34.85 MPa, which was ascribed to an increase in the internal porosity of the pastes.     

Reduction of lean NO2 with diesel soot over metal-exchanged ZSM5, perovskite and γ-alumina catalysts

The catalytic performances of metal-exchanged ZSM5, perovskite and γ-alumina catalysts for the reduction of nitrogen dioxide (NO₂) by diesel soot were investigated. The reaction tests were performed through temperature-programmed reaction (TPR), in which NO₂ and O₂ were passed through a fixed bed of catalyst-soot mixture. On the three types of catalyst, NO₂ was reduced to N₂ by model soot (Printex-U) and most of the soot was converted into CO₂. Pt-, Cu- and Co-exchanged ZSM5 catalysts exhibited reduction activities with conversions of NO₂ into N₂ of about 20%. Among the perovskite catalysts tested, La_0.9K_0.1FeO₃ showed a 32% conversion of NO₂ into N₂. The catalytic activities of the perovskite catalysts were largely influenced by the number and stability of oxygen vacancies. For the γ-alumina catalyst, the peak reduction activity appeared at a relatively high temperature of around 500 °C, but the NO₂ reduction was more effective than the NO reduction, in contrast to the results of the ZSM-5 and perovskite catalysts.     

Synthesis of a novel organic–inorganic hybrid flame retardant based on Ca(H2PO4)2 and hexachlorocyclotriphosphazene and its performance in polyvinyl alcohol

To optimize the poor thermal stability and flammable of polyvinyl alcohol (PVA), a novel environmental-friendly organic–inorganic hybrid flame retardant Ca(H₂PO₄)₂@HCCP was successfully designed and synthesized via surface treatment technology and used to advance the flame retardancy of PVA. The thermogravimetric analysis implied that Ca(H₂PO₄)₂@HCCP can enhance significantly the thermal stability and char forming ability of PVA. Combustion results demonstrate that Ca(H₂PO₄)₂@HCCP could effectively suppress the melt dripping of PVA in the process of combustion. The presence of Ca(H₂PO₄)₂@HCCP can sharply reduce peak heat release rate and the total heat release up to 75% and 22.9%, respectively, in the microscale combustion calorimeter measurement. The results manifested that Ca(H₂PO₄)₂@HCCP could endow PVA with superior flame retardancy. Moreover, char residues analysis explained the flame retardant mechanism in condensed and gas phase, which is mainly attributed to the strong catalytic char formation, free radical trapping, and gas barrier effect. Therefore, the green flame retardant has great applications prospect in fire safety.     

Preparation of organic–inorganic intumescent flame retardant with phosphorus,nitrogen and silicon and its flame retardant effect for epoxy resin

According to the requirement of fire life cycle assessment (LCA), chitosan ethoxyl urea phosphate (CEUP), an organic–inorganic intumescent flame retardant (IFR) containing phosphorus, nitrogen, and silicon, was synthesized by the reaction of chitosan, phosphorus pentoxide, and urea. FTIR, ¹H NMR, SEM, and XRD were employed to characterize the compounds. As a result, CEUP was successfully prepared with higher thermal stability, favorable to enhance fire resistance. Combined with OMMT, the organic/inorganic IFR was applied as EP flame-retardant agents. The combustion behavior of EP composite was investigated by LOI, UL-94, CCT, SEM, TGA, and TG-IR. It was observed that using 15% CEUP and 3% OMMT (EP3), LOI value reached 34.8% and passed the UL-94 V-0 rating, while THR and TSP of EP composite reduced 65 and 72% compared with pure EP. The char residue of EP composite was up to 22.4%. The thermal decomposition mechanism was traced from 100 to 600°C by TG-IR. It was suggestive that CEUP decomposition commenced at 100°C to create phosphoric acid and sublimation of urea occurred at 300°C. EP3 exhibited a strong thermal stability, namely even at 600°C, the volatile substances were detectable. Dense and expanded carbon layer was confirmed in SEM images.     

Comparison of Mg–Al layered double hydroxides intercalated with OH− and CO32− for the removal of HCl,SO2, and NO2

Journal of Porous Materials - Two different Mg–Al layered double hydroxides (LDHs), OH?Mg–Al LDH and CO3?Mg–Al LDH, are prepared and utilized for the efficient removal...     

Synthesis and catalytic activity of organic–inorganic hybrid catalysts coordinated with cobalt(II) ions for aerobic epoxidation of styrene

New organic–inorganic hybrid materials (HM) containing 3-mercaptopropyl groups (–(CH₂)₃–SH) have been synthesized through a dry gel conversion (DGC) route. The complex catalyst Co–HM was prepared through a simple coordination of –SH with cobalt(II) ions, which was firstly applied in the aerobic epoxidation of alkenes to obtain good results. Co–HM-50 exhibited the highest activity for the epoxidation of styrene with air to achieve 95.8 mol% of conversion with the epoxide selectivity of 89.2%. Recycling and control tests showed high durability and heterogeneity of Co–HM-50 as a heterogeneous catalyst.     

A new 3D Keggin-POM based metal–organic framework of Cu and H2biim: Assembly and properties of fluorescence and electrochemistry

A new 3D Keggin-based metal–organic framework consisting of two kinds of Cu-H₂biim chains, Cu₁₀(H₂biim)₁₀(PW₁₂O₄₀)₂(OH)₄·5H₂O 1 (H₂biim = 2,2′-biimidazole), has been synthesized under hydrothermal conditions. The TGA and PXRD measurements show that the framework is stable after removal of the guest water molecules. In addition, the luminescent and electrochemical properties of 1 have also been investigated.     

Multilayer organic–inorganic coating incorporating TiO2 nanocontainers loaded with inhibitors for corrosion protection of AA2024-T3

Organic–inorganic multilayer coating containing organically modified silicates, epoxy resins and TiO₂ nanocontainers loaded with 8-hydroxyquinoline were produced on AA2024-T3 substrates via dip coating method. The parameters of the curing temperature and time were optimized via variation in a widespread range in order to realize coatings with best anticorrosive properties. Curing temperature at 110 °C for 24 h presented the best anticorrosive behavior. The morphology of the coating was examined via scanning electron microscopy. The composition of the coatings was determined by energy dispersive X-ray analysis and Fourier transform infra-red spectroscopy. Furthermore, the coatings were exposed to corrosive environment and evaluated by electrochemical impedance spectroscopy. We demonstrate that the presence of loaded TiO₂ nanocontainers enhances the anticorrosive properties of the coatings; specifically, the total impedance values were increased about two orders of magnitude compare to the bare substrate after 400 h of exposure to aggressive environment.     

Electrooxidation of 2-chlorophenol and 2,4,6-chlorophenol on glassy carbon electrodes modified with graphite–zeolite mixtures

This work reports the behavior of zeolite–graphite electrodes for the oxidation of 2,4,6-trichlorophenol (2,4,6-TCP) and 2-chlorophenol (2-CP) in a pH 3, 0.5 M Na₂SO₄ electrolyte using cyclic voltammetry, chronoamperometry, electrochemical impedance and galvanostatic electrolysis. Three zeolites with different hydrophobic/hydrophilic balance were used, in order to determine the possible effect of this parameter. On glassy carbon (GC) modified with 80–20 % graphite–zeolite mixtures the voltammetric peak charge of 2-CP oxidation was higher than that on GC modified with graphite alone, clearly showing a catalytic effect of the zeolites. ZSM-5 was the more active zeolite, probably due to its hydrophobic character, which should favor its interaction with the also hydrophobic 2-CP. In agreement with this, the charge-transfer resistance of GC modified with a graphite-ZSM-5 mixture was about half that of GC modified with graphite alone, and its double-layer capacity about 50 % higher, indicating a modification of the interface which favours the reaction. On the contrary, for 2,4,6-TCP both the oxidation peak charge, and the charge-transfer resistance, for GC electrodes modified with graphite–zeolite mixtures was about the same as that of GC modified with graphite alone. This lack of catalytic action could be due to the fact that the oxidation of 2,4,6-TCP requires the release of at least one chlorine atom, this release being so difficult that it cannot be promoted by any of the zeolites studied. However, in prolonged galvanostatic electrolysis practically all the current went to the oxidation of 2,4,6-TCP, while in the case of 2-CP only a small fraction was oxidized. Probably with 2-CP at long times surface poisoning blocked the reaction, as reflected by the fact that the electrolysis potential rose to a value 0.2 V higher than that reached by TCP, and so high that most of the current went to oxygen evolution. The zeolites ZA and ZY decreased the mineralization of 2,4,6-TCP, since they promoted a one-electron oxidation reaction, so that its concentration at 80 min was about 80 % of that observed with graphite alone. The oxidation of 2-CP was not significantly affected by any zeolite as compared with that on graphite.     

Fischer–Tropsch synthesis over Co/TiO2 catalyst: Effect of catalyst activation by CO compared to H2

Co/TiO₂ catalyst activation for Fischer–Tropsch (FT) reaction by CO in comparison to H₂ has been performed. The catalyst, prepared by incipient wetness impregnation, has been characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses after separate reduction using CO and H₂ respectively. Temperature programmed reduction (TPR) analyses were also conducted to study the reduction behaviour of the catalyst in presence of H₂ and CO respectively. CO improved catalyst reduction and produced a more stable and active catalyst with higher selectivity and yield for C_5 + hydrocarbons at extended time-on-stream.     

Design of nitrogen-containing organic thermal stabilizer with resistance to “zinc burning” and its application

Using maleic anhydride and 6-amino-1,3-dimethyluracil as raw materials, by adding zinc oxide and introducing metal ions, the aminouracil zinc maleate (AM-Zn) was synthesized. The structure of the product was analyzed by Fourier transform infrared spectroscopy and ¹H NMR spectroscopy. The molecule contains ester group, carbon–carbon double bond, carboxylate and diazo group, which can be used as the main thermal stabilizer for poly(vinyl chloride) (PVC). The thermal stability and excellent resistance to zinc burning of AM-Zn were characterized by Congo red method, thermal aging method, thermal weight loss method, electrical conductivity, and other detection methods. In addition, the compound use of AM-Zn and CaSt₂ could further improve the thermal stability performance, which was excellent compared with the commercially available CaSt₂/ZnSt₂. The thermal stabilization effect was the best when CaSt₂/AM-Zn = 2:1, the initial whiteness could reach 50 min, and it was not completely blackened and aged within 80 min. The static stabilization time was 65 min, and the thermal stabilization time is increased by 40 min compared with CaSt₂/ZnSt₂. The thermal stabilization mechanism was analyzed, and the designed and synthesized AM-Zn, a multifunctional molecular structure, had a strong potential as a thermal stabilizer for PVC.     

Catalytic Removal of Toluene over Co3O4–CeO2 Mixed Oxide Catalysts: Comparison with Pt/Al2O3

The catalytic oxidation of toluene, chosen as VOC probe molecule, was investigated over Co₃O₄, CeO₂ and over Co₃O₄–CeO₂ mixed oxides and compared with the catalytic behavior of a conventional Pt(1 wt%)/Al₂O₃ catalyst. Complete toluene oxidation to carbon dioxide and water was achieved over all the investigated systems at temperatures below 500 °C. The most efficient catalyst, Co₃O₄(30 wt%)–CeO₂(70 wt%), showed full toluene conversion at 275 °C, comparing favorably with Pt/Al₂O₃ (100% toluene conversion at 225 °C).