Comparison between in-/injected-plasma catalysis for enhancing hydrocarbon selective catalytic reduction of NOx at low temperatures.

[Display omitted] • In-plasma is superior to injected-plasma catalysis for NO x removal at low temperatures. • Significant synergy between plasma and catalyst for NO x removal at low temperatures. • NO x removal efficiency up to 70% by assisting plasma at [200–250 °C] temperature. • Energy delivery through plasma is better than a thermal process for NO x removal. • Injected-plasma catalysis has potential applications in circumstantial high-throughput gas. Plasma-assisted hydrocarbon selective catalytic reduction (HC-SCR) of NO x was investigated by a packed Ag/γ-Al 2 O 3 catalyst in a dielectric barrier discharge reactor at low temperatures. The effect of plasma discharge on NO x removal was investigated with two methods for comparison, in- and injected-plasma catalysis systems. In-plasma catalysis comprised a plasma-catalytic discharge with the entire feed gas, and injected-plasma catalysis incorporated a part of feed gas consisting of dodecane pretreated with the plasma-catalytic discharge and mixed with the remaining gas before passing through the catalyst-alone stage. Here, using the surface response method with temperature and specific energy input (SEI) as independent variables, the results revealed that energy delivery through plasma gained more NO x removal efficiency than that by thermal catalyst process; a set of SEI and temperature is needed to obtain a similar level of NO x removal. There is a significant synergy between plasma and catalyst in in-plasma catalysis at low temperatures (≤250 °C) that increased NO x removal efficiency up to Δη = 50% (SEI = 137 J/L; T = 200 °C). In-plasma catalysis is superior to injected-plasma catalysis for enhancing the NO x removal and widening the temperature window of effective NO x removal owing to the plasma-catalytic interface in-plasma catalysis supplies. Interestingly, the results also revealed that the plasma in the catalyst for both methods did not always improve the NO x removal efficiency. The plasma had a negative effect on NO x removal at sufficient temperature and SEI. As a result, the in-plasma catalysis presented a high NO x removal efficiency; it can be higher than 70% at temperatures of 200–250 °C. However, injected-plasma catalysis has potential applications in circumstantial high-throughput gas due to low plasma energy consumption by adjusting the entire feed to plasma-treated gas ratio. [ABSTRACT FROM AUTHOR]