ABSTRACT
The abatement of NOx from mobile and stationary sources has become an important concern of industrialized countries, due to an increased attention to environmental pollution and to the demand for a sustainable energy development; it represents now a topical issue for environmental catalysis. Nitrogen oxides are mainly formed during the combustion of fossil fuels and biomasses. They are blamed for the production of acid rains, the formation of ozone in the troposphere, and for causing respiratory problems in humans. The mechanisms of formation of NOx are well known: (1) the reaction between N2 and O2 in air at high (flame) temperature according to the Zeldovich mechanism [1] (thermal NOx), (2) the oxidation of N-containing compounds in fuel or biomass (fuel NOx), and (3) the formation of intermediate HCN via the reaction of nitrogen radicals and hydrocarbons, followed by the oxidation of HCN to NO (prompt NOx). At high temperatures, thermal NOx usually represents most of the total NOx formed and typically consists of a mixture of 95% NO and 5% NO2 due to thermodynamics.
