The promotion effect of manganese on Cu/SAPO for selective catalytic reduction of NOx with NH3

The activity and hydrothermal stability of Cu/SAPO and xMn-2Cu/SAPO for low-temperature selective catalytic reduction of NOx with ammonia were investigated. An ion-exchanged method was employed to synthesize xMn-2Cu/SAPO, which was characterized by N-2 adsorption, ICP-AES, X-ray diffraction (XRD), NH3-temperature programmed desorption (NH3-TPD), NO oxidation, X-ray photoelectron spectrum (XPS), UV-vis, H-2-temperature programmed reduction (H-2-TPR) and diffuse reflectance infrared Fourier transform spectra (DRIFTS). 2Mn-2Cu/SAPO and 4Mn-2Cu/SAPO showed the best SCR activity, in that at 150 degrees C NO conversion reached 76% and N-2 selectivity was above 95% for the samples. NO oxidation results showed that the 2Mn-2Cu/SAPO had the best NO oxidation activity and the BET surface area decreased as manganese loading increased. XRD results showed that the metal species was well dispersed. NH3-TPD showed that the acid sites have no significant influence on the SCR activity of xMn-2Cu/SAPO. H-2-TPR patterns showed good redox capacity for xMn-2Cu/SAPO. UV-vis and H-2-TPR showed that the ratio of Mn4+ to Mn3+ increased as manganese loading increased. XPS spectra showed a significant amount of Mn3+ and Mn4+ species on the surface and addition of manganese increased the ratio of Cu2+. The promotion effect of manganese to 2Cu/SAPO comes from the generation of Mn3+ and Mn4+ species. Deduced from the DRIFTS spectra, the Elay-Rideal mechanism was effective on 4Mn-2Cu/SAPO.