The effect of various templates on the NH3-SCR activities over Cu/SAPO-34 catalysts

Abstract

The influence of various acid properties on the NH3-SCR activities was studied over four Cu/SAPO-34 catalysts, and these SAPO-34 supports were synthesized by various templates to generate diverse Si coordination structures. The XRD, SEM, NMR, NH3-TPD, NH3 oxidation and kinetic tests were used to characterize the Si coordination structures in SAPO-34 supports and their roles on the NH3-SCR activities. The 29Si NMR and NH3-TPD results showed that the template affected the Si coordination structures in SAPO-34 supports, and Si coordination structures further adjusted the acid properties and the Cu species distribution in Cu/SAPO-34 catalysts. The four Cu/SAPO-34 catalysts performed different NO conversions during 120–600°C though they contained the similar Cu loading by ion-exchange method. During the low temperature range, the kinetic results proved that various Si coordination structures did not affect the apparent activation energy (Ea) of NH3-SCR. But it was found that the acid densities were related to the NO conversions. In addition, the NH3 oxidation and NH3-SCR were competing reactions during the high temperature range, and the former one decreased the NO conversions in NH3-SCR for the competition of NH3 consumption. The strong acid sites could inhibit the NH3 conversions in NH3 oxidation, and it is found that the different Si coordination structures influenced the apparent activation energy (Ea) of NH3 oxidation over Cu/SAPO-34 catalysts. It was likely that the adsorbed NH3 species on the Brønsted acid sites showed more active in NH3-SCR than NH3 oxidation. Finally, the influence of various acid properties on NH3-SCR activities and the NH3 oxidation was concluded.