Control of NOx emissions from diesel engine by selective catalytic reduction (SCR) with urea

Among the catalysts screened, Cu-ion exchanged ZSM5 zeolite exhibited the highest NO removal activity, particularly at low reaction temperatures below 200 degreesC, maintaining a wide operating temperature window. The hydrothermal stability of the CuZSM5 catalyst can be improved by the optimization of metal content of the catalyst. Through the variation of reactor operating conditions, NO conversion of better than 90% could be achieved with a minimum NH3 slip. The decomposition of urea was also examined and a kinetic model for both thermal and catalytic decomposition of urea was developed. Urea-SCR over the CuZSM5 catalyst exhibited that the NO removal activity is competitive to that by NH3-SCR, indicating urea can be effectively utilized in SCR reactor system as the reducing agent.