Novel regenerated V- and Ce-mixed oxide modified catalysts for the NH3-SCR of NOx displaying a distinctive broad temperature window

Abstract

The challenge for selective catalytic reduction (SCR) of NOx with NH3 is to improve de-NOx activity at low temperatures while simultaneously improving the tolerance of catalysts towards SO2 poisoning. Herein, V and Ce oxides were loaded on deactivated SCR catalysts subjected to acid pickling (CAT) via impregnation to recover de-NOx activity. The resulting V–Ce@CAT catalyst exhibited 85–95% NOx conversions over a wide temperature window of 200–450 °C while conversions of only 40–78% over the same temperature range were observed with CAT (spent catalyst treated with acid). Interestingly, in addition to the high tolerance towards SO2 displayed by V–Ce@CAT, the catalyst exhibited improved reactivity after the introduction of 200 ppm SO2, with the NOx conversion increasing from 80% to 87%. The results indicated that a kinetic equilibrium was reached between the formation and decomposition rates of Ce2(SO4)3 on V–Ce@CAT which prevented the accumulation of surface sulfate species, thereby protecting the main active species V from catalytic inactivation. Furthermore, in situ DRIFTS revealed that the NH3-SCR reaction pathway of V–Ce@CAT follows the L-H mechanism.