Reduction of NOx by plasma-facilitated catalysis over In-doped γ-alumina

Sol–gel derived γ-alumina and its 2.5 wt.% indium doped derivative were examined as plasma-activated catalysts for reduction of NOx in model lean burn exhaust. The extent of promotional effect on catalysis due to indium doping depends both on the speciation of hydrocarbon used as a reducing agent in addition to reaction temperature. In/γ-alumina catalysts were tested with eight hydrocarbons (propane, propene, methanol, ethanol, 1-propanol, 2-propanol, acetaldehyde, isooctane) at a C1:N ratio of 12 to investigate the effect of hydrocarbon structure and chemistry on activity for plasma-enhanced catalysis. The functionality, the location of the functional group, as well as the molecular size all proved to have an impact on the ability of the hydrocarbon to participate in NOx reduction chemistry. Plasma assist provided benefits at moderate temperature, but NOx reduction was dominated by thermal activity (no plasma required) at high temperature. The effect of aging on catalyst performance was also examined, and the most negative impact on thermal activity was observed at moderate temperatures. Plasma assist resulted in recovery of nearly all activity for most of the oxygenated hydrocarbons examined. At high temperature, aging had negligible impact on catalyst performance with the exception of catalytic reduction with methanol.