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- Hansen, Staffan, et al.
(författare)
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Oxidation Catalysis on YBa2Cu3O6 + x
- 1988
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 334:6178, s. 143-145
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Tidskriftsartikel (refereegranskat)abstract
- Mild oxidation catalysts are used to product a wide range industrial chemicals from hydrocarbons, whereas deep oxidation catalysts yield CO2 and are becoming important in the cleaning of emissions from combustion of carbonaceous fuels. Here we report on a catalyst1 that facilitates both mild and deep oxidation of toluene in the presence of molecular oxygen and ammonia. At low partial pressures of O2a YBa2Cu3O6+x catalyst is very active in the formation of benzonitrile, but at higher O2 partial pressures it preferentially catalyses formation of CO2. This sharp transition in product selectivity is reversible and occurs at a defined partial pressure of O2. At transition the bulk compostition of the catalyst is close to YBa2Cu3O6 (x≈0). Increasing the content of lattice oxygen (x > 0) makes the catalyst selective for CO2 formation
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| 2. |
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| 3. |
- Otamiri, J, et al.
(författare)
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Kinetics and mechanisms in the ammoxidation of toluene over a V2O5 catalyst. Part 1: Selective reactions
- 1988
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Ingår i: Catalysis Today. - 0920-5861. ; 3:2-3, s. 211-222
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Tidskriftsartikel (refereegranskat)abstract
- A thorough kinetic investigation of the ammoxidation of toluene over a V2O5 catalyst was carried out. Pressures of reactants were varied and rates for formation of benzonitrile and benzaldehyde were determined. Kinetic expressions completely describing experimental data were derived. A mechanisms is proposed on basis of both rate equations and other types of information published in the literature. The (010) plane of V2O5 is considered to be the active plane. An ensemble of 4 V=O species, having neighbouring vanadium ions exposed, is the active site. The rate-determining step for formation of aldehyde is the abstraction of a hydrogen atom from the methyl group. Nitrile is formed from two routes. In one of the routes, the active site reacts with one ammonia molecule, which constitutes a rate-limiting step. In the second route, the active site chemisorbs two ammonia species, and the rate-determining step is the hydrogen abstraction from the methyl group. The results indicate that the electronic properties of the surface are greatly affected by adsorption of ammonia.
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| 4. |
- Otamiri, J, et al.
(författare)
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Kinetics and mechanisms in the ammoxidation of toluene over a V2O5 catalyst. Part 2: Non-selective reactions
- 1988
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 3:2-3, s. 223-234
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Tidskriftsartikel (refereegranskat)abstract
- In the ammoxidation of toluene over a V2O5 catalyst, the variation of initial rates with partial pressures of oxygen, toluene and ammonia was determined for formation of carbon oxides. Dependencies obtained were analyzed and expressed in terms of rate equations. It was found that CO and CO2 are initial products formed at different sites, none of which are involved in selective reactions. The mechanisms derived for the formation of the two oxides have many features in common. In each mechanism there are two parallel routes originating from the same active site, which is suggested to be an ensemble exposing vanadium ions and electrophilic oxygen species. One of the routes proceeds without participation of ammonia, while in the other route ammonia is adsorbed. In both routes, the rate-determining step can be considered to be one of the steps in a stepwise reoxidation process. The rates for formation of carbon oxides decrease strongly with increasing partial pressure of ammonia, which is due to a combined effect of introduction of a new reaction pathway and competitive adsorption between oxygen and ammonia.
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| 5. |
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