In situ DRIFT study on NH3 selective catalytic reduction of NOx over HBEA zeolite doped with CeO2

The reaction mechanism of selective catalytic reduction of NO with NH3 on Ce-doped HBEA catalysts was investigated using in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). The results illustrated that the amide species adsorbed on Lewis acid sites (AlO)(+) and NH4+ species adsorbed on Bronsted acid sites (Al-OH-Si) were main intermediates on HBEA. Only Eley-Rideal (E-R) mechanism was presented over HBEA catalyst. By contrast, both E-R and Langmuir-Hinshelwood (L-H) mechanism were presented over Ce(7.0)HBEA and the E-R mechanism was the dominated reaction mechanism. NH4+ adspecies and nitrate adspecies were primary intermediates on Ce(7.0)HBEA. Meanwhile, the presence of Ce3+ could lead to the increase of surface oxygen concentration, which could actively take part in the activation process of ammonia adspecies and NOx adspecies and then facilitated the NH3-SCR reaction. Hence, the NOx conversion of Ce(7.0)HBEA was much higher than that of HBEA. In addition, the surface oxygen vacancy derived from ceria on Ce(7.0)HBEA could inhibit the formation of N2O. As a result, the N-2 selectivity of Ce(7.0)HBEA is higher than that of HBEA. The above results are useful for guiding the way to develop Ce-containing SCR catalysts.