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

Journal article, 2014

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. Sol-gel prepared Ag/Al2O3 samples, with varying silver loading and doped with trace amounts of platinum, were evaluated as HC-SCR catalysts using n-octane as reductant 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 as the samples are doped with trace-amounts of platinum, the activity for lean NOx reduction at low temperatures is enhanced. The catalyst composition that displays the highest activity for NOx reduction is a 2 wt% 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. Adsorption of a higher amount of hydrocarbons could result in that a lower amount of reducing agent is required for Pt doped Ag-alumina catalysts as compared to un-doped ones, which is beneficial with respect to fuel efficiency.