NOx Reduction in Ag/Al2O3-SiO2 Converters in the Exhaust of a Compression-Ignition Engine

Abstract

NOx emissions in compression-ignition engines can be reduced, either through the application of engine-internal methods, i.e., making sure that as little NOx as possible is produced as a result of the mixture combustion processes, or through the use of catalytic converters designed to reduce nitrogen oxides, including NH3-SCR or HC-SCR converters. Converters using ammonia offer high conversion rates, but they tend to be problematic in terms of their operation. For this reason, converters using hydrocarbons for the purpose of NOx reduction have been gaining in popularity. An Ag/Al2O3-SiO2 converter is an example of such a catalytic converter. This paper describes the process of preparing such a converter and characterises the porosity and acidity of its surface. The dispersion of silver was assessed based on oxygen absorption tests on crystallites of sliver and based on TEM images of crystallites of silver. The conversion of NO2, NO and propane was assessed depending on the temperature. Additionally, NO2, NO and propane conversion was assessed at 500 °C, depending on the admixture of a reducer, and propane selectivity in the process of reduction of NO to N2 was calculated. The test results indicate that the developed converter can be considered the basis for further research into the development of this compression-ignition engine exhaust after-treatment technology.