Urea-related reactions and their active sites over Cu-SAPO-34: Formation of NH3 and conversion of HNCO.

Urea-SCR is an efficient method to reduce NO x emission from diesel vehicles, but the active sites of Cu-SAPO-34 for urea-related reactions have not been well identified. In the present work, a series of Cu-SAPO-34 catalysts with different copper species were prepared and tested for urea thermolysis, urea hydrolysis and urea-SCR. Temperature-programmed experiments and in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) were used to determine isolated Cu 2+ ions as the main active sites for these reactions. HNCO (isocyanic acid) and NH 3 are formed via urea thermolysis. HNCO is less active than NH 3 to interact with NO, and most of HNCO is hydrolyzed to produce NH 3 in urea-SCR. In the presence of NO 2 , the reactivity of HNCO as a reducing agent is promoted, but both HNCO-SCR and HNCO hydrolysis would be inhibited by the deposition of NH 4 NO 3 . These findings provide a foundation for improving deNO x efficiency of Cu-SAPO-34 catalysts on diesel vehicles. [ABSTRACT FROM AUTHOR]