Catalytic Oxidation of Volatile Organic Compounds with Mn-zeolites

Mn-catalysts supported on zeolites are active materials for oxidising volatile organic compounds, but the catalysts' activity and selectivity depend on the support's characteristics. In this work, we study the performance of different Mn catalysts supported on zeolites with different Si/Al ratios and topology in the ethanol oxidation reaction. The results show a correlation between the mechanism of the reaction and the presence or absence of acid sites on the zeolite surface, which is based on its aluminium content. It is observed that the presence of Brønsted acid sites catalyses ethanol dehydration to ethylene that is oxidised to CO2 at higher temperatures. Without protonic acid sites, ethanol is primarily oxidised to acetaldehyde and subsequently oxidised to CO2, achieving a complete oxidation at lower temperatures. The acidity also influences the nature of the metallic active sites, forming Mn-oxo species with higher oxidation state in the catalyst with lower aluminium content. These species are more active than those formed in the catalyst enriched with Brønsted acid sites. Thus, zeolites with higher Si/Al ratios are more adequate for supporting Mn catalysts in the ethanol oxidation reaction. The results show that low acidity is a decisive factor in designing active catalysts for this reaction, while zeolite topology or catalyst surface area are of secondary importance.