Activity of perovskite-based platinum doped catalysts in oxidation of organic air pollutants

Katalizatory tlenkowe oparte na tlenkach złożonych o strukturze perowskitu zazwyczaj wykazują wysoką aktywność w utlenianiu związków tlenopochodnych, natomiast zwykle są mało aktywne w utlenianiu węglowodorów, szczególnie aromatycznych. Do badań wykonano katalizatory na bazie perowskitu (LaMnO3), z dodatkiem platyny wprowadzonej do fazy aktywnej, na monolitycznym nośniku metalowym z warstwą pośrednią gamma-Al2O3. Przebadano je w utlenianiu toluenu oraz acetonu i octanu etylu, spalanych indywidualnie i w mieszaninach dwuskładnikowych - węglowodór i pochodna tlenowa. Wykazano, że utlenianie samego toluenu zachodziło do produktów końcowych - CO2 i H2O, natomiast związki tlenowe utleniały się poprzez produkty pośrednie - aldehyd octowy - w spalaniu obu związków oraz etanol - podczas spalania octanu etylu. W przypadku wszystkich katalizatorów niewielki wzajemny wpływ na spalanie każdego ze związków zaobserwowano spalając mieszaninę toluen-aceton, wyraźnie większy w przypadku mieszaniny toluen-octan etylu. Spalanie toluenu w mieszaninach na mniej aktywnych katalizatorach przebiegało poprzez benzen. W obecności obu katalizatorów dotowanych platyną, podczas spalania mieszanin stężenie aldehydu octowego zmalało, prawdopodobnie wskutek lokalnego wzrostu temperatury na platynie w wyniku spalenia toluenu. Najwyższą aktywność wykazał katalizator z dodatkiem platyny wstępnie naniesionej na gamma-Al2O3, o ogólnej zawartości czynnika aktywnego 20% mas. Stwierdzono, że minimalna zawartość czynnika aktywnego w przypadku katalizatorów tlenkowych nie powinna być mniejsza niż 15% mas.Metal oxide perovskite-type catalysts usually show high activity for oxidizing oxy-derivative compounds, but they are much less active in the oxidation of hydrocarbons, particularly aromatics. For the purpose of the study, LaMnO3-based catalysts, with platinum incorporated into the active phase, were prepared on monolithic metallic supports washcoated with gamma-Al2O3. The catalysts were tested in the oxidation of toluene, as well as acetone and ethyl acetate, which were combusted separately or in two-component mixtures - hydrocarbon and oxy-derivative. It has been demonstrated that when toluene alone was oxidized, the reaction ran to final products - CO2 and H2O, while oxygen compounds were oxidized via intermediate products - acetaldehyde during combustion of both compounds, and ethanol during combustion of ethyl acetate. With all the catalysts tested, the "mixture effect" of each component was insignificant during oxidation of the toluene-acetone mixture, and noticeably stronger during combustion of the toluene-ethyl acetate mixture. The combustion of toluene in mixtures over catalysts of lower activity occurred via benzene. In the presence of Pt-doped catalysts, the concentration of acetaldehyde during combustion of mixtures decreased, which was probably due to a local rise in temperature on the Pt active sites as a result of toluene oxidation. The highest activity was that of the catalyst where platinum was deposited onto gamma-Al2O3, and the total content of the active phase amounted to 20 wt. %. It has been found that in the case of metal oxide catalysts the minimal content of the active phase can not be lower than 15 wt. %

Activity and selectivity of metal oxide catalsts on monolithic or granular supports in the oxidation of typical organic air pollutants

The aim of the study was to compare the activity and selectivityof metal oxide catalysts on monolithic or granular supports in the oxidation of toluene and three oxyderivatives-acetone,ethyl acetate and butyl acetate.Four catalysts were manufactured for the purpose of the study-two with perovskite and two with Cu-Zn oxides as active phases,on a cordierite support in the from of a monolith or irregular grains.The shape of the catalyst support did not affect catalytic activity,but it hod an influence on the reaction selectivity in the oxidation of the oxyderivatives.In the presence of Cu-Zn catalysts,more products of incomplete oxidation were obtained for the monolithicshape,and thier concentrations were higher than those for the granular catalyst.For perovskite catalysts an inverse relation was observed.With such discreancy between the results it is impossible to make and generalization on the contribution of the support shape to the selectivity of the catalyst

Activity of LaMnO3perovskite monolithic catalyst in the oxidation of selected volatile organic compounds

Wytworzono monolityczny katalizator perowskitowy (LaMn03) i jego aktywność przebadano w reakcji utleniania wybranych lotnych związków organicznych. Badania prowadzono w reaktorze przepływowym przy obciążeniu 10000 h-1 i stężeniu utlenianych związków - 1 g/m3. Najwyższą aktywność katalizatora uzyskano w utlenianiu połączeń tlenopochodnych - etanolu i acetonu, oraz węglowodoru alifatycznego - heptanu, nieco niższą w utlenianiu octanu etylu, najniższą natomiast w utlenianiu związków aromatycznych - toluenu i ksylenówMonolithic perovskite catalyst LaMnO, was manufactured and tested for activity in the oxidation of selected volatile organic compounds. Tests were conducted in a quartz cross-flow reactor for the space velocity equal to 10 000 h-1 and the concentration of each oxidized compound - 1 g/m3. Prepared catalyst Showed high activity in the oxidation of oxy-derivatives - ethanol and acetone* and aliphatic hydrocarbon - n-heptane, lower in the oxidation of ethyl acetate. The lowest activity of catalyst was found for aro¬matic hydrocarbons oxidation - toluene and xylenes

Activities of perovskite and palladium catalysts in the oxidation of organic air pollutants

One of the advantageous methods for the control of VOC emission is their catalytic oxidation. In the study reported in this paper, hydrocarbons of choice and oxygen compounds were combusted alone or in mixtures over two monolithic catalysts - a perovskite catalyst (PER-Ag) and a palladium catalyst (M-2). It was only in the oxidation of toluene vapours that M-2 showed a noticeably higher activity than did PER-Ag. There was no difference in the activity between the two catalysts in the oxidation of ethanol and n-hexane, but PER-Ag performed much better in the oxidation of ethyl acetate and acetone. Although the presence of oxygen compounds practically did not affect the performance of M-2 in the combustion of toluene and n-hexane at temperatures higher than 380°C there was a distinct inhibiting effect when the hydrocarbons were combusted over PER-Ag. The presence of hydrocarbons did not very much influence the conversion of oxy-derivatives over M-2 or PER-Ag (over the latter only above 300°C). Toluene had an influence on the selectivity of the reaction to acetaldehyde when the oxy-derivatives were oxidized - over both catalysts the concen-trations were higher than when the oxy-derivative compounds were combusted alone. In the presence of n-hexane, no intermediate products of ethyl acetate and acetone oxidation were yielded over PER-Ag