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Volume 143, Issue 1 , September 1993 , Pages 275-285
2007, Microporous and Mesoporous Materials
2007, Journal of Molecular Catalysis A: Chemical
2006, Journal of Molecular Catalysis A: Chemical
Chinese Journal of Catalysis, Volume 35, Issue 6, 2014, pp. 922-928
Applied Catalysis B: Environmental, Volume 199, 2016, pp. 523-530
Chemical Physics Letters, Volume 609, 2014, pp. 88-92
Computational and Theoretical Chemistry, Volume 1018, 2013, pp. 6-12
Journal of Contaminant Hydrology, Volume 183, 2015, pp. 99-108
Journal of Environmental Chemical Engineering, Volume 1, Issue 4, 2013, pp. 822-830
Copyright © 1993 Academic Press. All rights reserved.
The synthesis and catalytic properties of V-NCL-1, a novel vanadium silicate, large-pore molecular sieve in various oxidation reactions, are described. The reactions include the oxidation of n -octane, cyclohexane, toluene, trimethylbenzenes, and naphthalene. In the as-synthesized form, most of the vanadium in V-NCL-1 is present as atomically dispersed and isolated V 4+ located in framework positions, though not necessarily in tetrahedral coordination. On calcination in air, the vanadium ions are oxidized to the pentavalent state. In addition, part of the vanadium leaves lattice locations and forms nonframework clusters. When the oxidized sample is reduced, V 4+ ions are formed again. The three-dimensional silicate structure of the molecular sieve is intact during all these treatments. Due to the presence of large pores. V-NCL-l is able to oxidize bulky molecules such as mesitylene and naphthalene. Unlike their titanium analogs, vanadium silicates are able to oxyfunctionalize the primary carbon atoms in alkanes and the side chains in alkylaromatics.
This work reports the synthesis and characterization of mixed oxide vanadium–manganese V 2 O 5 /K-OMS-2 at various V/Mn molar ratios and prepared by the impregnation method. Characterization of these new composite materials was made by elemental analysis, BET, XRD, FT-IR, SEM and TEM techniques. Results of these analyses showed that vanadium impregnated samples contained mixed phases of cryptomelane and crystalline V 2 O 5 species.
Oxidation of various alcohols was studied in the liquid phase over the V 2 O 5 /K-OMS-2 catalyst using tert -butyl hydroperoxide (TBHP) and H 2 O 2 as the oxidant. Activity of the V 2 O 5 /K-OMS-2 samples was increased considerably with respect to K-OMS-2 catalyst due to the interaction of manganese oxide and V 2 O 5 .
The kinetic of benzyl alcohol oxidation using excess TBHP over V 2 O 5 /K-OMS-2 catalyst was investigated at different temperatures and a pseudo-first order reaction was determined with respect to benzyl alcohol. The effects of reaction time, oxidant/alcohol molar ratio, reaction temperature, solvents, catalyst recycling potential and leaching were investigated.
Since the discovery of titanium silicalite more than 30 years ago, framework metal-containing zeotype materials have become an important class of catalyst, finding application in several industrial processes. Incorporation of cations of titanium, tin, iron, and other elements into zeotype frameworks (and also into ordered mesoporous materials) has led to both scientific progress and engineering innovations in catalysis. As a result of these developments, framework metal-containing zeotype materials have been implemented in the preceding decade in new commercial, by-product-free green processes, which have improved sustainability in the chemical industry. Based on a comprehensive analysis of the recent literature including patents, this review is a summary of the current knowledge of the science and technology of framework metal-containing zeotype materials. The synthesis of these materials is summarized, followed by an account of state-of-the-art characterization results. The key catalytic chemistries, which can be classified into oxidation reactions such as olefin epoxidation, aromatic hydroxylation and ammoximation, and weak Lewis acid-catalyzed reactions, are discussed. Mechanisms proposed for these transformations are reviewed, together with the theoretical and modeling tools applied in this context. An overview of the technologies associated with the use of framework metal-containing zeotype materials demonstrates how these processes are linked with each other through key chemicals involved.
Nickel substituted copper chromite spinels (Cu 1− x Ni x Cr 2 O 4 , where x = 0, 0.25, 0.5, 0.75 and 1.0) were prepared by homogeneous co-precipitation method. The materials were characterized in detail by X-ray diffraction, BET surface area, scanning electron microscopy, energy dispersive X-ray analysis and FTIR spectroscopy. Powder X-ray diffraction pattern reveals the spinel phase formation and energy dispersive X-ray analysis indicates the correct stoichiometry. Liquid-phase oxidation of ethylbenzene using TBHP (70%) as an oxidant shows that the catalysts are highly active. Leaching studies performed by hot filtration experiments and reusability studies show that nickel substituted copper chromite spinels are stable under the reaction conditions.
This paper reports the one-step ambient-temperature synthesis of porous vanadosilicates by using tetraethyl orthosilicate as a silicon source, V 2 O 5 powder as a vanadium source, and long-chain n -alkylamine (C 8 –C 12 ) as a structure directing agent. The texture of the materials was characterized by powder X-ray diffraction, N 2 adsorption–desorption isotherms, transmission electron microscopy, and thermogravimetric and differential thermal analysis. The pore size of the vanadosilicates depended largely upon the chain length of n -alkylamine. The n -alkylamine with longer carbon chain was advantageous for the formation of the larger pores. The Si/V ratio was another key factor affecting pore size of the vanadosilicates. When n -dodecylamine was employed as a structure directing agent, only mesopore structure vanadosilicates were obtained. However, when n -decylamine was used, the pore diameter of the vanadosilicates underwent a change from mesoporous scale to super-microporous scale through changing the Si/V molar ratio. The vanadosilicates exhibit a large BET specific surface area and a good thermal stability. The Si/V molar ratios of both mesoporous and super-microporous vanadosilicates with the relatively uniform pore channels could be reached 10.0 or even below. The vanadosilicates with a Si/V ratio in the range of 8.5–12 synthesized by using either n -dodecylamine or n -decylamine have a high thermal stability beyond 823 K. The nature of vanadyl species in the vanadosilicates was investigated with the use of several characterization techniques. It was determined by Raman, H 2 -TPR and ESR that both V V O x and V IV O x species were coexisted in the calcined vanadosilicates. The V V O x species occurred mainly in a form of monomeric tetrahedral vanadyl species on the pore wall, having one V O bond and three bridging V O Si bonds linked with the framework. The V 4+ centers were in an isolated octahedrally-coordinated V IV O x mode. It was interesting to find that only a small part of V IV O x species existed in the as-synthesized vanadosilicates, while a large part of V IV O x species were formed upon calcination in air.
Tin-containing ordered mesoporous silica materials (Sn-OMS) were synthesized by two different routes, viz. by the direct hydrothermal method (Sn–MCM-41, Sn–MCM-48) and by the grafting method (Sn/MCM-41, Sn/MCM-48, Sn/SBA-15). The materials were characterized in detail by ICP-OES analysis, XRD, FTIR, N 2 adsorption–desorption, SEM and UV–vis analysis. The catalytic activity of the tin-modified mesoporous materials was ratified in the Meerwein–Ponndorf–Verley reduction of carbonyl compounds using secondary alcohols (2-butanol and 2-propanol) as hydrogen transfer agents. A comparison of catalytic activities of tin-containing mesoporous materials prepared by the two routes, dictates that tin-grafted mesoporous materials show higher catalytic activity than the tin incorporated mesoporous catalysts, even though both the materials had similar tin loadings. Among the tin-grafted catalysts, the samples prepared using the tin precursor, Me 3 SnCl, showed better activity than the other precursors Bu 3 SnCl, Ph 3 SnCl and Ph 2 SnCl 2 and among the mesoporous supports, Si–MCM-41 shows better catalytic results than the other supports like Si–MCM-48 and Si–SBA-15.
Zirconium doped manganese oxide OMS-2 materials have been synthesized. The synthesized zirconium doped manganese oxide OMS-2 materials have been characterized by XRD, TGA, BET and TEM techniques. All the materials showed the OMS-2 type (cryptomelane) X-ray diffraction patterns and the thermal stability and BET surface area of zirconium doped OMS-2 materials are improved compared to the parent manganese oxide (K-OMS-2) material. Transmission electron micrographs showed the rod like needle shaped morphology and zirconia dispersion on fibrous morphology of as-synthesized zirconium doped manganese oxide OMS-2 materials. As synthesized zirconium incorporated OMS-2 catalysts have been tested for the liquid phase oxidation of side chain aromatic compounds (ethylbenzene and benzyl alcohol) and cyclohexanol. Zr-K-OMS-2 (Cry) has shown high conversion for ethylbenzene and benzyl alcohol, whereas Zr-K-OMS-2 (Bir) has shown high activity for the conversion of cyclohexanol and good selectivity towards the formation of cyclohexanone.
N-doped graphene materials were prepared from both inorganic and organic nitrogen sources and pyrolytic graphene oxide as the carbon substrate. Transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to investigate the detailed growth mechanism of the N species in these N-doped graphene materials. The different chemical nature and binding energy of the different N species resulted in their different trends with annealing temperature. These N-doped graphene are excellent catalysts in the oxidation of ethylbenzene. A high yield of acetonphenone did not depend on the total nitrogen amount but only on the type of nitrogen species. Too much defects and N-dopants were detrimental to this reaction. A proper activation of the oxidant is needed to get good catalytic activity.
Biomass gasification combined with effective gas cleaning is an interesting way to produce energy or syngas for numerous applications. ZrO 2 -based catalysts have been proven to remove the undesired tar molecules when a convenient oxygen amount is added. The oxidation of toluene (a tar model compound) was addressed in this work by applying temperature-programmed surface reaction (TPSR) experiments with a continuous feed of toluene and oxygen. Complete toluene conversions were achieved over all zirconia-based catalysts (ZrO 2 , Y 2 O 3 -ZrO 2 and SiO 2 -ZrO 2 ) in toluene oxidation above 550 °C (toluene WHSV 0.06–0.07 1/h). Toluene was oxidized into four products (CO 2 , H 2 O, CO and H 2 ). The formation of incomplete oxidation products (CO and H 2 ) suggests that these catalysts are able to convert undesired tar molecules also into valuable synthesis gas components. Increasing the oxygen amount increased the product ratio of CO 2 and CO. Over pure ZrO 2 , the formation of CO and H 2 was detected at 600 °C even with the highest feed ratio of O 2 /TOL (≈3.5 × theoretical toluene total oxidation ratio), while over the doped zirconias the formation of CO and H 2 approached zero with increasing temperature and over-stoichiometric feeds. Separate CO oxidation experiments confirmed different but appreciable activities of different zirconia materials for that reaction. However, a very minor water-gas shift activity in the presence of oxygen was detected only over pure ZrO 2 at the studied temperature range. The collected multiresponse reaction data was subsequently subjected to transient kinetic modeling established on hypotheses of surface reaction mechanisms (Part B: Kinetic modeling).
Magnetite is an iron oxide widely used as contrast agent in MRI, receiving considerable interest from nanoscience and nanotechnology. In this work, the face 1 0 0 of the magnetite structure was studied with water in order to obtain 1 H hyperfine coupling constants (HFCCs). Molecular dynamics (MD) calculations were performed using the ReaxFF program and for statistical inefficiency, structures were selected for HFCC and NMR calculations. From our theoretical findings, the magnetite in solution considerably increases the 1 H HFCC of water molecules. From our results, it is essential to incorporate the dynamics and solvent effects into NMR calculations of relaxation parameters.
The reaction mechanism of nitric oxide with four hydroxycyclohexadienyl peroxyl radicals from the oxidation of benzene in the troposphere has been investigated using the UB3LYP/6-311++G(d,p) density functional theory (DFT) method. The title reaction was found to involve five steps and produce the following intermediates and products: cis -peroxynitrite, trans -peroxynitrite, hydroxycyclohexadienyl nitrate, 2-hydroxy cyclohexadienyl oxyl radical, 3-hydroxy-1,2-epoxy-5-cyclohexene radical (and NO 2 ), hexa-2,4-diene-1,6-dial ( trans -HONO), hydroxyl-cyclohexadienone (HNO 2 ). The results confirm that aromatic compounds contribute to tropospheric ozone production, the rain acidity, and secondary organic aerosol (SOA) pollution via the title reaction with a sufficiently high concentration of NO x .
In Situ Chemical Oxidation (ISCO) based on the Fenton's process is a proven technology for the treatment of groundwater contaminated by organic compounds. Nevertheless, the application of this treatment process to methyl tert-butyl ether (MtBE) is questioned, as there are concerns about its capacity to achieve complete mineralization. Many existing studies have focused on water contaminated by MtBE and are thus not representative of in situ treatments since they do not consider the presence of soil. In this work, the effectiveness of a Fenton-like process for MtBE treatment was proven in soil column tests performed at operating conditions (i.e., oxidant and contaminant concentration and flow rates) resembling those typically used for in situ applications. No MtBE by-products were detected in any of the tested conditions, thus suggesting that the tert-butyl group of MtBE was completely degraded. A mass balance based on the CO 2 produced was used as evidence that most of the MtBE removed was actually mineralized. Finally, the obtained results show that preconditioning of soil with a chelating agent (EDTA) significantly enhanced MtBE oxidation.
In order to assess the degradation of aromatic compounds in fog, the reaction of benzene with hydroxyl radicals was studied in a bulk aqueous system. The effects of temperature, oxygen content, ionic strength, and pH were investigated in a batch reactor by following the two main products, phenol and biphenyl. The reaction rate increased with temperature, but was not significantly affected by ionic strength and pH. The overall phenol yield also did not significantly change with the removal of oxygen from the system. Conversely, the formation of biphenyl was more favorable under conditions of low oxygen content, high ionic strength, and low pH. The pH of the solution decreased during the reaction due to the formation of oxidation products of phenol; thus, we found that biphenyl did not form in detectable concentrations unless the pH was at or below 4.50–4.80.
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