Improved low-temperature activity of silver-alumina for lean NOx reduction – effects of Ag loading and low level Pt doping

Karl  Gunnarsson, Chalmers University of Technology

ORAL PRESENTATION: This study focuses on the effect of silver loading and low-level platinum doping on the distribution of silver species, the hydrocarbon activation, and the low-temperature activity for lean NOx reduction over silver-alumina catalysts. Ag/Al2O3 samples, prepared by a sol-gel based method, including freeze-drying with varying silver loading and doped with trace amounts of platinum, were evaluated as HC-SCR catalysts using n-octane in a synthetic gas-bench reactor. In addition, the samples were characterized using X-ray photoelectron spectroscopy, ultraviolet visible spectroscopy, and the specific surface area was determined using nitrogen sorption.
The study shows that Ag-alumina catalysts prepared via the sol-gel based synthesis method display a high consistency regarding specific surface area and ratio between different silver species, as the silver loading is increased. Furthermore, it is concluded that as the samples are doped with trace-amounts of platinum, the activity for lean NOx reduction at low temperatures is enhanced. The catalyst composition which shows the best activity for NOx reduction is found to be a 2 wt% loaded Ag/Al2O3 sample doped with 500 ppm platinum. This catalyst displays the highest low-temperature activity, most likely owing to an increased ability to adsorb and partially oxidize the hydrocarbon reductant, which is attributed to the Pt doping. A higher hydrocarbon adsorption could mean that a lower amount of reducing agent would be required for Pt doped Ag-alumina catalysts as compared to un-doped ones, which is beneficial with respect to fuel efficiency.