Speciation of Cu Cations in Cu-CHA Catalysts for NH3-SCR: Effects of SiO2/AlO3 Ratio and Cu-Loading Investigated by Transient Response Methods

Abstract

We develop an experimental protocol to quantify the speciation of Cu ions (ZCuIIOH and Z2CuII) in Cu-CHA catalysts for the NH3 Selective Catalytic Reduction of NOx (NH3-SCR). Toward this end, we performed four transient tests, namely H2-TPR, NO + NH3 TPR, NO2 adsorption + TPD, and NH3 adsorption + TPD, over two sets of Cu-CHA research catalysts characterized by different Cu contents (0–2.1% w/w) and SiO2/Al2O3 (SAR) ratios (10–25). Preliminary H2-TPR tests on the samples with the extreme SAR and Cu loading values were used to identify the variability range of the fractions of ZCuIIOH and Z2CuII species in these catalysts. The ZCuIIOH fraction was found to vary between 0.55 (at Cu/Al = 0.11) and 0.79 (at Cu/Al = 0.29). NO+NH3 TPR runs demonstrated that the NO + NH3 mixture is a much stronger reducing agent than H2: full reduction of all the Cu was obtained already at lower temperature, and differences in the reducibility of ZCuIIOH and Z2CuII were strongly attenuated. Both the integral NO consumption and t...