Combination of low and high temperature catalytic materials to obtain broad temperature coverage for plasma-facilitated NOx reduction

Two catalysts, Ba/zeolite Y and Ag/(gamma)-alumina, were combined to reduce NOx in simulated lean exhaust using plasma-facilitated catalysis. Steady-state experiments conducted at 473, 623, and 773 K show that ordering of the catalysts impacts NOx conversion, and maximum efficiency is obtained when the zeolite material precedes the alumina. Optimal ordering results in greater than 80% conversion at 473 K, and efficiencies greater than 95% were obtained at 623 and 773 K under steady operation when propene was added as a reductant at C1:NOx=12. Temperature cycling experiments covering the temperature range 373–773 K were used to determine a ‘transient’ cycle efficiency of 70% for the optimal catalyst configuration. Results of these experiments suggest that preferred ordering likely results in better management of stored NOx when transients to higher temperature occur. Studies also show that improved hydrocarbon utilization is evident in the optimal configuration due to the nature of the partially oxidized hydrocarbons that are formed at various stages of during the plasma-facilitated catalytic NOx reduction process.