Understanding the Ag/Al2O3 hydrocarbon-SCR catalyst deactivation through TG/DT analyses of different configurations

Understanding the parameters affecting the Ag/Al2O3 hydrocarbon SCR catalyst activity or the procedure by which the C-containing species are deposited on the catalyst surface, under actual diesel engine operation, can lead to design a low temperature active Ag/Al2O3 SCR catalyst. In this work we investigated the role of the Ag/Al2O3 HC-SCR catalyst configuration for NOx reduction activity and its deactivation by coking under passive and active operation. This was done by separating the powdered catalyst into two layers/partitions (front and rear). The single and double-layered catalysts were exposed to real diesel engine exhaust gas, and then thermo gravimetric (TG) and differential thermal (DT) analyses were carried out. The analysis showed that the retention of carbon-rich species (hydrocarbons and soot) in the double-layered configuration occurs mainly in the first catalyst layer (front layer), therefore resulting in a cleaner second layer (rear layer). The results confirm that the catalyst deactivation initiated at the front part of the catalyst and progressively spreads towards the back. TG/DT analyses also showed that the retention of carbon-rich species over the catalysts was strongly reduced at temperatures higher than 350 °C or when hydrogen was introduced, but the deactivation pattern was similar. The reactor design (e.g. catalyst configuration) in HC-SCR with silver is an important factor, and in the presented work the space in between the beds shown to be a critical parameter as it enhanced the low temperature catalytic activity.