Influence of phosphorus on Cu-SSZ-13 for selective catalytic reduction of NOx by ammonia

Abstract

The influence of phosphorus on Cu-SSZ-13 NH3-SCR catalysts was investigated in order to reveal the deactivation behavior of Cu-SSZ-13 in the presence of phosphorus-containing poisons in the exhaust of diesel engines. The phosphorus-poisoning was simulated by treating the Cu-SSZ-13 catalysts with (NH4)2HPO4 aqueous solution using incipient wetness impregnation method. The focus of the study was the effect of phosphorous on the different reactions occurring on the SCR catalyst, including ammonia oxidation, NO oxidation and standard SCR using monolith catalysts. Moreover, characterization such as ICP-SFMS, N2-physisorption, and NH3-TPD were employed for the evaluation of the physical and chemical properties of the P-impregnated catalysts. Physically blocking of pores and poisoning of acidic sites were observed on the P-impregnated catalysts. In addition, we observed that phosphorus severely suppressed ammonia oxidation and NO oxidation, while its impact on standard SCR reaction was nearly negligible below 300°C. Interestingly, a promotive effect was found at higher temperatures, likely due to the severely inhibiting effect on NH3 oxidation caused by the formation of copper phosphates in the large cages (i.e. 8-membered rings) of Cu-SSZ-13.