Vapor Phase Oxidation Of Toluene Research Articles

Oxidation of Toluene on Supported and Unsupported LaCoO3 Perovskites Catalyst

Perovskite type oxide are known to be catalysts for a number of reactions such as total and partial oxidation, hydrocracking, hydrogeneous, hydrogenolysis and reduction etc. Efforts has largely been directed towards synthesis of unsupported and supported perovskites oxides of moderates or high specific area, their bulk and surface properties and their role in heterogenous catalysis. Oxidation of aromatic and aliphatic hydrocarbon over LaMO3 (M=Al, Ni, Mn, Co, Fe, Cr etc.) perovskites have been studied. Vapour phase catalytic oxidation of toluene over perovskites Viz., LaCoO3, LaCoO3/ SiO2 and LaCoO3/Al2O3 has been studied. The characterization of the catalyst was carried out using technique Viz. I.R., Surface area, Packing density. Surface acidity, Surface basicity. The surface area measurements in the temperature range 350ºC to 600ºC. The maximum surface area & maximum activity was observed at 450ºC. The heterogeneous catalytic vapour phase oxidation of toluene give benzaldehyde, benzoic acid, maleic acid and CO2 as products over LaCoO3 and LaCoO3 supported on Al2O3 and SiO2 as catalyst. The LaCoO3 supported on Al2O3 has been found to be the most active and selective catalyst giving 84.0% selectivity for benzaldehyde at 450⁰C with surface area 78.9m2/g. The overall Kinetic analysis indicate that the oxidation of Toluene to benzaldehyde is first order. The order of catalytic reactivity is LaCoO3/Al2O3 > LaCoO3/ SiO2 > LaCoO3.

Vapour phase oxidation of toluene over CeAlPO-5 molecular sieves.

Single-site CeAlPO-5 with Al/Ce ratios 25, 50, 75, 100 and 125 were synthesized hydrothermally in fluoride medium. The XRD patterns of CeAlPO-5 exhibited characteristic reflections of AlPO-5. 27Al MAS-NMR of CeAIPO-5(25) showed two unusual peaks at -20.78 and -71.35 ppm due to delocalization of cerium unpaired electron. However, 31P MAS-NMR exhibited the usual characteristic peak similar to that of AlPO-5. Vapour phase oxidation of toluene in air over CeAlPO-5 yielded benzaldehyde with high toluene conversion. The time on stream study established the stability of the catalyst. This catalyst can also be used for the selective oxidation of other alkyl aromatics.

Vapour phase oxidation of toluene in V/Al 2O 3–TiO 2 catalytic reactors

The catalytic membrane reactor and the inert packed bed membrane reactor were studied in the vapour phase selective oxidation of toluene. Different feeding policies for the membrane were explored and their influence on the selectivity to the desired products (benzaldehyde and benzoic acid) was investigated. The active phase was prepared by depositing vanadium on a Al 2O 3–TiO 2 support prepared through the sol–gel technique. Higher selectivity to benzaldehyde was obtained using the catalytic membrane reactor. Differences were seen in the catalytic membrane reactor performance only when the active phase was heavily charged along the membrane cross-section.

Catalytic oxidation of toluene with molecular oxygen over Cr-substituted mesoporous materials

The syntheses of thermally stable chromium-incorporating hexagonal mesoporous aluminophosphate and cubic Cr-MCM-48 have been reported. Characterization of the catalysts was made using low angle XRD, N 2 adsorption, UV-VISDRS, thermal analysis, ICP-AES and ESR. Mesoporous Cr-AlPO 4 and Cr-MCM-48 catalysts have been found to be active for the vapour phase oxidation of toluene with molecular oxygen. Mesoporous Cr-AlPO 4 is found to exhibit both acidic and redox properties and hence oxidation as well as dealkylation reactions are taking place in a concerted manner, whereas, the cubic silicate analogue acts as a pure redox catalyst.

The effect of alkali metal promotion on vanadium-containing catalysts in the vapour phase oxidation of methyl aromatics to the corresponding aldehydes

The comparison of vanadium phosphate catalysed ammoxidation with the oxidation of methyl aromatics to the corresponding nitriles and aldehydes showed significant differences in catalytic performance. The ammoxidation proceeds with nearly complete conversion and high nitrile selectivities, whereas the partial oxidation of the same feed to aldehydes under similar conditions leads to poor activity and selectivity only. This result is supposed to be due to the lack of a sufficient basicity in the reaction system; catalyst surface acidity causes strong reactant–solid interaction that is the reason for consecutive overoxidation. Therefore, potassium-containing vanadium phosphates and more basic alkali cation-containing vanadia solids (M/V 2O 5, M=Li, Na, K, Rb, Cs) were synthesised and used as catalysts in the vapour phase oxidation of toluene (TO), p-methoxytoluene (MTO) and p-chlorotoluene (CTO) to the corresponding aldehydes. Moreover, the effect of the addition of a non-oxidisable base (e.g. pyridine) to the reaction mixture was studied. Parent catalyst samples and used specimens were characterised by X-ray diffractometry and infrared spectroscopy. Vanadates and bronze phases of the more bulky alkali metal cations are generated during catalyst synthesis and catalytic reaction that may lead to new surface arrangements with vanadia. The catalytic results showed that alkali metal-containing vanadia catalysts revealed significant higher performance compared to vanadium phosphate solids. The increasing alkali cation size and basicity in the order from Li to Cs leads to an increase in the aldehyde selectivity. The effect of acid–base properties of catalyst bulk and surface in connection with reactant nucleophilicity and the impact of electronic effects of the substituents on the catalytic behaviour are discussed.

Comparative study of vanadium aluminophosphate molecular sieves VAPO-5, -11, -17 and -31

Vanadium aluminophosphate molecular sieves VAPO-5, -11, -17 and -31 were synthesized hydrothermally and fully characterized using XRD, A.A, SEM, N 2 and n-butane adsorption, diffuse reflectance UV-Vis, XPS, 27 Al , 31 P , 51 V NMR and ESR techniques. XRD data of VAPOs were consistent with their corresponding AlPOs structural patterns and indicated that all VAPOs were very well crystallized. The 51 V NMR spectra of calcined air-exposed (hydrated) VAPOs samples revealed that vanadium cations are present as V 5+ both in distorted octahedral and tetrahedral coordination and quite probably in a framework position. DRS UV-Visible spectroscopy shows that in low vanadium content calcined samples, V 5+ ions are mostly in tetrahedral coordination without any presence of polymeric extraframework oxy-vanadium phase. ESR and XPS spectroscopies indicated the presence of residual V 4+ in calcined samples. VAPOs were found to be active in vapor phase oxidation of toluene with molecular oxygen. VAPO-11 and -31 showed high oxidation catalytic activity and selectivity for benzaldehyde. The order of activity were VAPO-11 > VAPO-31 > VAPO-5 ≥ VAPO-17. VAPO-11 better selectivity is related to its unique structural properties compared to those of the other VAPOs synthesized in this study.

Changes in properties of V 2O 5–K 2SO 4–SiO 2 catalysts in air, hydrogen and toluene vapors

V 2O 5–K 2SO 4–SiO 2 catalysts were studied by TG, DTA, TPR and XRD methods. During activation NH 4VO 3 and (COOH) 2, used for impregnation of the support, decompose in air below a temperature of 350°C. Over 350°C oxidation of vanadium up to V 5+ and changes in the catalyst reducibility occur. In TPR using pure hydrogen, the freshly activated catalyst is reduced in three steps. The first peak with a maximum around 430°C is a result of reduction of the vanadium oxide species. The second and the third TPR peaks correspond mainly to the reduction of sulfate species to H 2S. It was found that vanadium oxides noticeably enhanced the reduction of sulfate to H 2S. Similar TPR profiles were found after catalytic tests (vapor phase oxidation of toluene by air) and after reduction of the same catalyst by H 2, and its reoxidation by air in some particular conditions. By increasing temperature and prolonging time of activation, or by prolonging time-on-stream of toluene oxidation the reducibility of vanadium oxides decreases and the easily reducible part of sulfate species is converted into a less reducible part.

Selective oxidation of toluene to benzoic acid catalyzed by modified vanadium oxides

A variety of oxides were examined as additives to a V 2O 5/TiO 2 catalyst in order to enhance the catalytic performance for the vapor phase oxidation of toluene to benzoic acid. It was found that the modification with SeO 2, TeO 2 or Sb 2O 3 greatly promoted the title reaction leading to improved catalyst performance in terms of toluene conversion and benzoic acid selectivity. The effect of reaction temperature, O 2/toluene ratio, steam/toluene ratio and durability were also investigated in order to reveal the catalytic features of the modified catalyst systems.

Promoted TiO2 (Anatase)-Supported Vanadium Oxide Catalysts. TPR Study and Activity in Oxidation of Toluene

Vanadium oxide doped with K, Li, Bi, Sb, Te, U or Mo oxide, supported on TiO2 - anatase, was studied by temperature programmed reduction (TPR). The influence of the addition of promoters (up to molar ratio M : V = 0.5) to 5 wt.% V2O5/TiO2 catalyst on the TPR profile is presented in correlation with their catalytic activity in the vapor phase oxidation of toluene. All promoters, except Bi2O3, decrease the catalyst reducibility and decrease the rate of the toluene oxidation. A strong negative influence on the activity of the toluene oxidation have K, Li, and Te oxides. However, the presence of all tested promoters in the molar ratio M : V = 0.05 has a positive effect on the selectivity of benzoic acid formation. A further increase of this ratio leads to a decrease of the selectivity in the case of U, Mo and mainly K oxides, while with Li, Bi, Sb, and Te oxides, the selectivity remains almost unchanged. No correlation between TPR profiles of doped catalysts and their selectivity was found. The most effective promoter of vanadia catalysts for the benzoic acid production is Sb oxide, possessing a very high selectivity at high conversion of toluene.

Oxidation of toluene to benzoic acid over modified V2O5-TiO2 catalyst with SeO2, TeO2 and Sb2O3

It was found that the addition of SeO2, TeO2 or Sb2O3 to a V2O5/TiO2 catalyst greatly improved the catalytic activity in the vapor phase oxidation of toluene to selectively form benzoic acid.

Oxidation of toluene on lanthanum cobaltite perovskite (LaCoO3) catalyst

Vapor phase oxidation of toluene to benzaldehyde has been studied on lanthanum cobaltite, LaCoO3, with a perovskite structure. Experimental data were obtained in the temperature range 350 to 600°C and contact time 0.2 to 2 h. The overall kinetic analysis indicated the oxidation of toluene to benzaldehyde to be first order, with a frequency factor of 0.62 h−1 and an activation energy of 38.29 kJ mol−1.

Heterogeneous vapor phase oxidation of toluene over V2O2·SnO2 catalyst

The vapor phase oxidation of toluene over V2O5·SnO2 catalyst was studied in a microreactor operating at atmospheric pressure. The overall kinetic analysis indicated the oxidation reaction to be first order with a frequency factor of 1.88×108 s−1 and an activation energy of 168.5 kJ mol−1. The catalysts with both V2O5 and V6O13 were especially active and selective. The composition of SnO2 phase was found to be V0.03Sn0.97O2·SnO2 weakens the short V=O bond.

Ferric molybdate—A catalyst for the oxidation of toluene

Production of benzaldehyde has been carried out by vapour phase oxidation of toluene over silica supported ferric molybdate catalyst, at different support/ catalyst ratio. The temperature, concentration of the catalyst and space-velocities were varied over a wide range with each catalyst. The best results were obtained with ferric molybdate (60%) supported on SiO2 at a temperature of 450°C, space velocity 10373±20 litre hour−1 litre−1, air/toluene ratio 610 and volume of the catalyst 20 cc. The yield of benzaldehyde on the basis of toluene reacted is 70·2% per pass, total conversion 34·9% and conversion to benzaldehyde is 24·5%, surface area and pore size structure of the catalyst was determined by gravimetric method using quartz fibre spring technique.

Vapour phase oxidation of toluene by ozone

During vapour phase oxidation of toluene with ozone, oxy-groups may be added to the aromatic nucleus. At a temperature of up to 200° and with a contact time of about 0·03 the rate of formation of aromatic products containing oxygen shows a linear relation with partial pressure of ozone in an ozone-oxygen mixture and is practically independent of partial oxygen pressure in the mixture.