Catalytic oxidation of toluene with molecular oxygen over Cr-substituted mesoporous materials
TL;DR: In this article, a series of mesoporous ma-terials with pore dimensions greater than 20A have been synthesized using structure-directing templates and they have been found to be active for the vapourphase oxidation of toluene with molecular oxygen.
Abstract: Thesynthesesofthermallystablechromium-incorporatinghexagonalmesoporousaluminophosphateandcubicCr-MCM-48have been reported. Characterization of the catalysts was made using low angle XRD, N 2 adsorption, UV-VISDRS, thermalanalysis, ICP-AES and ESR. Mesoporous Cr-AlPO 4 and Cr-MCM-48 catalysts have been found to be active for the vapourphase oxidation of toluene with molecular oxygen. Mesoporous Cr-AlPO 4 is found to exhibit both acidic and redox propertiesand hence oxidation as well as dealkylation reactions are taking place in a concerted manner, whereas, the cubic silicateanalogue acts as a pure redox catalyst.© 2002 Elsevier Science B.V. All rights reserved. Keywords: Chromium; Aluminophosphates; Mesoporous materials; Partial oxidation 1. IntroductionAluminophosphate materials, recently developed ascrystalline microporous materials are of potential useincatalysis[1].Flanigenetal.[2]reportedtheincorpo-ration of various elements into the framework sites ofaluminophospahtes and the resulting systems are ac-tiveforvariouscatalytictransformations.However,thepore dimensions of these materials are not sufficient toaccommodate a broad spectrum of organic moleculesin their cavities. With the first discovery of M41S bythe Mobil researchers, a series of mesoporous ma-terials with pore dimensions greater than 20A havebeen synthesised using structure-directing templates
Citations
More filters
TL;DR: Significant enhancement of the response and selectivity to o-xylene and toluene is attributed to the decrease in the hole concentration in NiO and the catalytic oxidation of methyl groups by Cr doping.
Abstract: Ultraselective and sensitive detection of xylene and toluene with minimum interferences of other indoor air pollutants such as benzene, ethanol, and formaldehyde is achieved using NiO hierarchical nanostructures doped with Cr. Pure and 1.15–2.56 at% Cr-doped NiO flower-like hierarchical nanostructures assembled from nanosheets are prepared by a simple solvothermal reaction and their gas sensing characteristics toward o-xylene and toluene gases are investigated. The 1.15 at% Cr-doped NiO hierarchical nanostructures show high responses to 5 ppm of o-xylene and toluene (ratio of resistance to gas and air = 11.61 and 7.81, respectively) and negligible cross-responses to 5 ppm of benzene, formaldehyde, ethanol, hydrogen, and carbon monoxide. However, pure NiO nanostructures show low responses to 5 ppm of o-xylene and toluene (ratio of resistance to gas and air = 2.01 and 1.14, respectively) and no selectivity toward any specific gas is observed. Significant enhancement of the response and selectivity to o-xylene and toluene is attributed to the decrease in the hole concentration in NiO and the catalytic oxidation of methyl groups by Cr doping.
221 citations
TL;DR: Highly active catalysts for oxidative dehydrogenation of ethane with CO2 were characterized by temperature-programmed reduction (TPR), temperature- programmed oxidation (TPO), Fourier transform infrared (FTIR) spectroscopy, and X-ray absorption fine-structure (XAFS) analysis.
Abstract: Highly active catalysts for oxidative dehydrogenation of ethane with CO2 were characterized by temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), Fourier transform infr...
125 citations
TL;DR: In this paper, the pH of the impregnation solution influences the surface charge of the mesoporous support and therefore determines the strength of interaction between the cobalt precursor and the support.
Abstract: Cobalt-containing MCM-41 and SBA-15 mesoporous materials were prepared by the pH-adjusting of the impregnation solution. The modified materials were investigated by X-ray diffraction, N2 physisorption, temperature-programmed reduction, DR UV–Vis diffuse reflectance, and FT-IR spectroscopy of adsorbed pyridine. The pH of the impregnation solution influences the surface charge of the mesoporous support and therefore determines the strength of interaction between the cobalt precursor and the mesoporous support. The formation of different cobalt oxide species in different ratios, depending on the pH of the impregnation solution, was established for both materials. The modified Co/MCM-41 and Co/SBA-15 materials were active in toluene oxidation. Their catalytic activity is predetermined by the nature, the reducibility, and the dispersion of the obtained cobalt oxide species.
78 citations
TL;DR: ZSM-5-supported chromium oxide catalysts prepared by an incipient wetness method have been tested for the dehydrogenation of propane to propylene in the presence of carbon dioxide as discussed by the authors.
76 citations
TL;DR: In this paper, an ultraselective and selective detection of methyl benzenes was achieved for Co 3 O 4 nanorods through Cr-doping, which significantly enhanced the response to methyl benzene while suppressing cross-responses to interfering gases.
Abstract: Ultrasensitive and selective detection of methyl benzenes was achieved for Co 3 O 4 nanorods through Cr-doping. Pure and 1.17–1.89 at% Cr-doped Co 3 O 4 nanorods were synthesized by a solvothermal reaction, followed by calcination at 400°C for 2 h. The gas-sensing properties of the nanorods were tested to methyl benzene (toluene and xylene) and compared with interfering gases (benzene, ethanol, ammonia, CO and NO 2 ) at various concentrations (0.25–5 ppm) and temperatures (250–350°C). The results demonstrated that Cr-doping significantly enhanced the response to methyl benzenes while suppressing cross-responses to interfering gases, resulting in selectivity for methyl benzene. The ultraselectivity to methyl benzene in the Cr-doped Co 3 O 4 nanorods was attributed to catalytic activity and the abundant adsorbed oxygen of the Cr oxides and Co 3 O 4 for the partial oxidation of methyl benzenes to more active chemical species. Keywords: gas sensor; xylene; toluene; selectivity; Cr-doped Co
75 citations
Cites background from "Catalytic oxidation of toluene with..."
...It is worthwhile to note that Cr2O3 is known to promote the oxidation of methyl groups to the corresponding ketones and acids [37] and thus it has been used as another promising catalyst to remove toluene via oxidation [38-41]....
[...]
References
More filters
TL;DR: A neutral templating route for preparing mesoporous molecular sieves is demonstrated based on hydrogen-bonding interactions and self-assembly between neutral primary amine micelles (S�) and neutral inorganic precursors (l�).
Abstract: A neutral templating route for preparing mesoporous molecular sieves is demonstrated based on hydrogen-bonding interactions and self-assembly between neutral primary amine micelles (S degrees ) and neutral inorganic precursors (l degrees ). The S degrees l degrees templating pathway produces ordered mesoporous materials with thicker framework walls, smaller x-ray scattering domain sizes, and substantially improved textural mesoporosities in comparison with M41S materials templated by quaternary ammonium cations of equivalent chain length. This synthetic strategy also allows for the facile, environmentally benign recovery of the cost-intensive template by simple solvent extraction methods. The S degrees 1 degrees templating route provides for the synthesis of other oxide mesostructures (such as aluminas) that may be less readily accessible by electrostatic templating pathways.
1,733 citations
Book•
01 Oct 1988
TL;DR: In this article, the authors present an interpretation of phase diagram for phase diagrams and demonstrate the properties of the phase diagram in terms of magnetic and optical properties, as well as non-stoichiometry.
Abstract: Crystal Structures. Bonding in Solids. Crystallography and Diffraction Techniques. Other Techniques: Microscopy, Spectroscopy, Thermal Analysis. Crystal Defects, Non--Stoichiometry and Solid Solutions. Interpretation of Phase Diagrams. Electrical Properties. Magnetic and Optical Properties. Synthesis Methods. Further Reading. Appendices. Questions. Index.
631 citations
"Catalytic oxidation of toluene with..." refers background in this paper
...This could be due to a large difference in LFSE between these two geometries [20]....
[...]
TL;DR: In this article, a hexagonal mesostructured aluminophosphates (APW-2) is formed by transformation of a layered precipitate composed of both alumnophosphate oligomers and alkyltrimethylammonium cations.
Abstract: Lamellar and hexagonal mesostructured aluminophosphates (AlPOs) were prepared and characterized. The lamellar mesostructured AlPO (APW-1) formed hydrothermally and the condensed framework was composed of alternating AlO4 and PO4 units. The hexagonal mesostructured AlPO (APW-2) is formed by transformation of a layered precipitate composed of both aluminophosphate oligomers and alkyltrimethylammonium (ATMA) cations. Calcined APW-2 had a mesoporosity with the BET surface area of 980 m2 g-1 and a pore diameter of 1.8 nm after substantial shrinkage of the framework. Lamellar APW-1 formed under most of the conditions surveyed, while hexagonal APW-2 was obtained under very restricted conditions. In this system, the charge matching in the products is the most important factor, although the assemblies of ATMA cations are essential as the structure-directing agents.
104 citations
TL;DR: In this article, the behavior of Cr was investigated spectroscopically by diffuse reflectance spectroscopy (d.r.s.) and electron spin resonance (e.s.s.).
73 citations
TL;DR: In this paper, the spectral properties of CrO43− ion in Ca2PO4Cl (chlorospodiosite) single crystals confirm the structural results established by single-crystal x-ray structure analyses.
Abstract: Studies of the spectral properties of CrO43− ion in Ca2PO4Cl (chlorospodiosite) single crystals confirm the structural results established by single‐crystal x‐ray structure analyses. Detailed electron spin resonance measurements of a single crystal of Ca2(PO4, CrO4)Cl are described and the appropriate spin‐Hamiltonian parameters determined. It is shown that the unpaired electron (3d1) in its ground state occupies a dz2 orbital, which is largely concentrated on the chromium atom. The visible and ultraviolet absorption spectrum of a single crystal of Ca2PO4Cl containing CrO43− is described and shown to be similar to the spectrum of MnO42−, which had been interpreted on the basis of a Ballhausen and Liehr molecular‐orbital level scheme. The infrared absorption spectra show more splitting of the vibrational bands of the chromate (V) compound (Ca2CrO4Cl) than of the phosphate (Ca2PO4Cl), in agreement with the structural results which indicated a greater distortion of the CrO43− than that of the PO43− tetrahedr...
67 citations