Toluene total oxidation

Fe-Co layered double hydroxides with Co/Fe ratios of 2 and 3 were prepared with or without the presence of Beta zeolite and their catalytic potential was tested in toluene total oxidation. These calcined solids synthesised with p-zeolite were less active and selective than those prepared without zeolite. However, a mechanical mixture of 1/3 Fe,Co-LDH (Co/Fe = 3) + 2/3 NaP-zeolite presented higher catalytic performance which could be explain by a synergetic effect of the both Fe,Co-double oxide and p-zeolite. The mechanism could undergo through a spillover of the adsorbed toluene from zeolite, which has a high toluene storage/release capacity, to the Fe,Co double oxide, which is highly performant for this oxidation. 

Pure perovskites are active catalysts for toluene complete oxidation and LaCoOs is a good example. Toluene total oxidation on these catalysts is conducted for only nonnoxious CO2 without any CO or by-products formation [26]. Such behavior is obviously assigned to the capacity of the transitional metal to change the oxidation state, while the rare earth element is considered to remain unaffected during the catalytic process. 

In the last decade, different authors have studied the use of different wash-coats, which act as a host for the active palladium component, to prepare monolithic catalysts for toluene total oxidation. 263, CejcYi cOz, Ce cZri cOz, Ceo.8Zro.i5Lao.o50<5, Ceo.gZro.zOz and Ceo.4Zro.4Yo.iMno.iO(5 have all been... 

Characterisation of new Pd / hierarchical macro-mesoporous ZrOa, Ti02 and Zr02-Ti02 catalysts for toluene total oxidation... 

Titanium oxide nanotubes (TNTs) have been synthesized via laboratory-made Ti02 A and commercial Ti02 P25. 1.5wt% gold or palladium were deposited on TNTA and TNTP25 supports and the catalytic activity was evaluated in propene, methyl ethyl ketone (MEK) and toluene total oxidation. The catalytic properties of supported TNT were correlated with the structural pecuharity and the nature of the TNT, but also with the nature of the noble metal and the kind of the VOC. 

The ignition curves for propene, MEK and toluene total oxidation over gold and palladium catalysts are shown in Figs. 2 (A, B, C). For propene oxidation the observed products are only carbon dioxide and water, indicating complete combustion occttrring during the reaction. However it is found that toluene and MEK oxidations to CO2 are... 

The exceptional renewed interest in supported gold catalysts leads us to mention here a few recent examples of the formation of in situ gold carbonyl species from supported gold that can be related to the preparation of supported Au nanoclusters [53-55]. On the other hand, bimetallic carbonyl cluster salts of [Au4Fe4(CO)i,5] and [AuFe4(CO)i,5] have been used recently in the preparation of Au/Fe0,t/Ti02 catalysts for the total oxidation of dichlorobenzene and toluene [56]. 

Toluene can be readily ammoxidized to benzonitrile, usually over supported vanadium oxide and vanadium phosphate catalysts [e. g. 9,57]. Besides catalyst choice, catalytic performance mainly depends on the reaction conditions. Excess ammonia, as mentioned above, significantly increases nitrile selectivity by blocking sites responsible for consecutive oxidation ammonia also frequently reduces catalyst activity [1]. Water vapor in the reactant stream can also improve selectivity by blocking sites for total oxidation [38] or providing Brdnsted sites for the activation of ammonia [51]. 

P-23 - Total oxidation of volatile organic compounds - catalytic oxidation of toluene over CuY zeolites... 

Transformation of toluene in low concentration (800 ppm) in air over CuY zeolites containing different copper contents and Si/Al ratios was studied at temperatures between 150 and 500°C. It was found that total oxidation is promoted on non dealuminated catalysts and depends on the copper content. The most active catalysts correspond to the catalysts with Cu contents that are close to the complete exchange of the zeolite. The presence of sodium cocations in CuY zeolites increases their combustion efficiency, by improving the dispersion of ionic copper species and preventing the formation of CuO clusters. 

The maximum growth rates and the turnover coefficients for toluene and o-xylene used in the model were obtained from batch experiments with organisms that were isolated from the same soil columns (Meckenstock, 1999 Morasch et al., 2001). The constant decay rate was adjusted so that the microbial growth and decay dynamics derived from the observed reactive species behaviour could be reproduced. The value of the Monod-constant for toluene was adapted to result in the observed residual toluene concentrations. A low value was taken for the Monod-constant for sulfate so that sulfate concentrations will not limit microbial growth. The stoichiometric factor for sulfate consumption was calculated from the underlying redox equations for a total oxidation of the substrates to CO2. 

The topmost layer in Fig. 5.18 is made up of the neutral coordinatively saturated cations in the (001) surface for the layered V2O5 bulk material. In contrast, the (110) surface is formed by the cleavage of covalent V-0 bonds at the surface, thus resulting in coordinatively unsaturated V and 0 atoms at its side faces as shown in Fig. 5.18. The less reactive (001) surface is thought to be responsible for the selective oxidation of hydrocarbons such as toluene, whereas the reactive (110) surface predominantly results in total oxidation. This surface is also easily hydroxylated and, hence, contains both Brpnsted acid and base sites. 

Toluene is a representative example of aromatic compounds investigated due to its extensive use in industrial processes as solvent or as feedstock for the production of polymers or adhesives, but also due to its existence in petroleum-derived fuels. In a close relation, catalytic total oxidation takes into consideration the serious environmental concern generated by its perilous health effects but also by its contribution to global warming smog processes as a result of the emission of toluene from both stationary and mobile sources. 

Scheme 18.1 Cooperative electron delocalization effects between Eu and Fe in EuFeOs perov-skite for total oxidation of toluene. (Reprinted with permission from Ref. [25]. Copyright 2014, Elsevier.)...

Other related perovskite catalysts for total oxidation of toluene are mixed Co2Mn4Al2 oxides with high specific surface areas prepared via thermal decomposition of hydrotalcites. These catalysts contain in fact a mixing of nanocrystallites of Co-spinel, MnsOg, and CoMnOg phases that exhibit redox properties [29]. 

In another attempt, highly dispersed Zr02 and Xi02 were covered by manganese oxides by means of reactions in molten Na(K)NOs fluxes at 500 °C [37]. Mn (III, IV) species produced from the reaction in the melt were active in the total oxidation of benzene and toluene as it has been confirmed by T o values of 236 and 167 °C for benzene and toluene oxidation, respectively. 

The role of support on the performance of noble metals-based catalysts for the total oxidation of aromatic hydrocarbons is essential [38]. Although with a smaller surface area than the typical supports, perovskites also demonstrate good properties as carriers for noble metals. Thus, perovskites of type LaBOs (B = Co, Mn, Fe, Ni) synthesized using the citrate route were used as support for noble metals in total oxidation of toluene [39]. The performances of these catalysts varied in the order Fe>Mn>Co>Ni, and the superior behavior of iron was attributed to the low temperature of calcination and the high stability of the perovskite lattice irrespective of the nature of the stream it was exposed to. The dispersion of palladium at the different stages of the process remained unchanged. 

More complex in preparation and expensive, hierarchically nanostructured porous group V metal oxides synthesized via a spontaneous autoformation process from alkoxide precursors were used as supports for palladium in total oxidation of toluene (Figure 18.8) [40]. In addition to the effect of the support cation, multimodal porosities of these supports facilitate both the dispersion of the noble metal nanoparticles and the internal transport of the substrates. 

Ozone acts as the precursor of the key oxidants in the toluene decomposition. The presence of water vapor is also very important, as has been demonstrated for the catalytic oxidation of benzene with ozone on supported manganese Oxides catalysts [68]. It suppresses the catalyst deactivation by inhibiting the buildup of organic by-products on the catalyst surface, including formic acid and strongly bound surface formates. Scheme 18.2 proposes a general pattern mechanism for the plasma-driven total oxidation of the hydrocarbons. 

P. (2009) La(i ,)Sr Coi. Fey03 perovskites prepared by sol-gel method characterization and relationships with catalytic properties for total oxidation of toluene. Appl. Catal B Environ., 88 (3-4), 438 7. 

Florea, M., Alifanti, M., Parvulescu, V.I., Mihaila-Tarabasanu, D., Diamandescu, L., Feder, M., Negrila, C., and Fnmza, L. (2009) Total oxidation of toluene on ferrite-type catalysts. Catal. Today, 141 (3-4), 361-366. 

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