In this study, Copper supported on SAPO-34 molecular sieves or alumina is prepared via an incipient wetness impregnation method for ammonia selective catalytic reduction (NH3-SCR). These NH3-SCR catalysts are characterized by pulse chemisorption, temperature-programmed reduction (TPR), and temperature-programmed desorption (TPD) with three different conditions (NH3, NO, combined NH3-NO) to evaluate the adsorption of ammonia and nitric oxide. Cu/SAPO-34 catalyst has shown higher ammonia adsorption capacity compared to Cu/Al2O3 catalyst. The Cu/SAPO-34 adsorption is enhanced due to the strong acidity and high surface area of SAPO-34 molecular sieves. NO adsorption peaks over both catalysts are small (for NO-TPD) and these peaks become broader when a combined NH3-NO is introduced to the system.
However, Cu/SAPO-34 & Cu/Al2O3 surface area and acidity are decreased dramatically comparing to SAPO-34 and Al2O3 supports. These observations are verified by TPR and CO chemisorption. The formation of bulk copper aluminate over (Cu/Al2O3) surface and CuO over (Cu/SAPO-34) surface may block the acid sites. Moreover, the metal dispersion over both catalysts is below 10%.
Based on the comparison, various factors could influence the adsorption of NH3 and NO over the catalyst surface. The high specific surface area could provide abundant adsorption sites, which increase the adsorption capacity. Also, the multiple locations of acid spots along a wide temperature range, which are seen over Cu/SAPO-34, could continuously maintain the adsorption of NH3 and NO even at elevated temperature
