NH3 Oxidation Mechanism over Cu/SAPO-34 Catalysts Prepared by Different Methods

摘要

NH3 oxidation mechanism and its inhibition effect on the selective catalytic reduction of NOx by NH3 (NH3-SCR) reaction over two series of Cu/SAPO-34 catalysts were studied. It was found that the different NO conversions were induced by the diverse NH3 oxidation degree. X-ray diffraction, scanning electron microscopy, H-2 temperature-programmed reduction (H-2-TPR), and CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) analyses were conducted to estimate the Cu species distribution. The TPR results showed that the CuO species was dominant in impregnated Cu/SAPO-34 samples, and the ion-exchanged Cu/SAPO-34 samples contained more isolated Cu2+ species. Furthermore, H-2-TPR, electron paramagnetic resonance, and CO-DRIFTS analyses were utilized to quantify the CuO, Cu2+, and Cu+ species. The results together with the kinetic results revealed the CuO is the active site for NH3 oxidation, and the NH3 oxidation over Cu/SAPO-34 sample consists two steps: (a) NO production; (b) further NO consumption by adsorbed NH3 species on Cu2+ sites. Finally, the inhibition of NH3 oxidation on NH3-SCR activity was explained and the NO conversion at high temperature was related to the Cu2+/CuO ratio in Cu/SAPO-34 sample.