LaFe xMn yMo zO 3 catalysts for the oxidation of volatile aromatic organic contaminants

Abstract

Novas perovskitas mistas LaFe x Mn y Mo z O 3 foram preparadas, caracterizadas e investigadas como catalisadores para a oxidação total de tolueno, usado como composto orgânico aromático volátil (COV aromático) modelo. As perovskitas foram caracterizadas por DRX (Difratometria de Raios X), RTP (Redução a Temperatura Programada), determinação de área superficial BET e espectroscopia Mössbauer. Os dados obtidos indicaram a formação da fase perovskita e a incorporação de todos os metais na estrutura. As reações catalíticas foram realizadas em um sistema de Reação a Temperatura Programada com tolueno (1000 ppm) e ar sintético em fase gasosa. Foi observado que a oxidação do tolueno inicia-se a 280 o C e que Mn é o principal responsável pela atividade catalítica. No entanto, a presença de pequenas quantidades de Fe (LaFe 0,27 Mn 0,73 O 3 ) resulta em um importante aumento nessa atividade. Estudos de tempo de vida mostraram que os catalisadores são estáveis mesmo após 100 h de reação a 400 o C e nenhuma alteração estrutural significativa foi observada por DRX e Mössbauer.New mixed perovskites LaFe x Mn y Mo z O 3 were prepared, characterized and investigated as catalysts for the total oxidation of the model aromatic VOC (Volatile Organic Compound), toluene. The perovskites were characterized by XRD (X-Ray Diffractometry), Mössbauer spectroscopy, TPR (Temperature Programmed Reduction) and BET surface area determination. The results suggested the formation of the perovskite phase with incorporation of all metals in the structure. The catalytic studies were carried out in a Temperature Programmed Reaction system with toluene (1000 ppm) and synthetic air in the gas phase. It was observed that the oxidation of toluene starts at temperature as low as 280 °C and that Mn is responsible for most of the catalytic activity. However, the presence of small amounts of Fe (LaFe 0.27 Mn 0.73 O 3 ) leads to an increase in this activity. Stability studies showed that these perovskite catalysts are stable even after 100 h reaction at 400 o C with no significant structural change, as observed by XRD and Mössbauer analyses.Keywords: lanthanum iron perovskite, toluene oxidation, catalytic oxidation, manganese, molybdenum IntroductionPerovskite type oxides, ABO 3 , have been extensively investigated as catalysts for several processes including fuel cells, 1 water dissociation, 2 hydrogenation and hydrogenolysis, 3 ammonia oxidation 4 and NO x reduction. 5 Several reviews covering these fields can be found in the literature. 6,7 Perovskites, especially LaMnO 3 , have also been used in environmental applications, e.g. the oxidation of hydrocarbons, 8-10 chlorinated organics 11 and H 2 O 2 reactions. 6,12 LaMnO 3 shows good stability and flexible oxygen stoichiometry ( ) with different Mn oxidation states, i.e. Mn 2+ , Mn 3+ , Mn 4+ , which strongly affects the catalytic behavior. Also, the isomorphic substitution of metals in the perovskite structure allows a control of the catalytic properties of the material. Several LaMnO 3 1525 Tristão et a...

Iron: a versatile element to produce materials for environmental applications

“…62,63 Magnetite showed a high activity for the oxidation of carbon monoxide at lower temperatures, being related to the presence of surface Fe 2+ species capable of activating gas phase O 2 to form more reactive species. 64,65 Magnetite doped with Mn or Co, Fe 3-x M x O 4 (M = Mn, Co; x = 0-0.75) was also used as catalyst to high selective oxidation of β-pinene, a renewable monoterpene, under solvent free conditions.…”

“…The improvement of the catalytic activity was discussed in terms of the effect of Fe on the creation of surface and structural defects which can increase the perovskite reactivity towards oxygen. 63,65 Iron was also used as catalyst associated with materials such as clays. The pillared clay montmorillonite containing highly dispersed iron oxide showed very good activity and stability for the oxidation of toluene.…”

Catalytic oxidation of toluene on Ce–Co and La–Co mixed oxides synthesized by exotemplating and evaporation methods

“…In this work, Co oxide was used as the coupling species with cerium or lanthanum in Co-Ce or Co-La mixed oxides. Cerium oxide is often used for VOC oxidation, either as a support or mixed with other metal oxides [4,16,[42][43][44][45][46][47][48][49][50][51][52][53]; however not many studies are found in literature for lanthanum oxides [54][55][56][57][58]. The obtained catalysts were tested in the oxidation of toluene (C 7 H 8 ), which has a vapour pressure of 2.734 kPa at 20°C [59].…”