Stability Mechanism of Low Temperature C₂H₄–SCR with Activated-Carbon-Supported MnO_x-Based Catalyst

Abstract

Manganese-based catalysts have shown great potential for use as a hydrocarbon reductant for NO x reduction (HC-SCR) at low temperatures if their catalytic stability could be further maintained. The effect of CeO 2 as a promoter and catalyst stability agent for activated carbon supported MnO x was investigated during low temperature deNO x based on a C 2 H 4 reductant. The modern characterization technology could provide a clear understanding of the activity observed during the deNO x tests. When reaction temperatures were greater than 180 °C and with ceria concentrations more than 5%, the overall NO conversion became stable near 70% during long duration testing. In situ DRIFTS shows that C 2 H 4 is adsorbed on the Mn 3 Ce 3 /NAC catalysts to generate hydrocarbon activated intermediates, R-COOH, and the reaction mechanism followed the E-R mechanism. The stability and the analytical data pointed to the formation of stable oxygen vacancies within Ce 3+ /Ce 4+ redox couplets that prevented the reduction of MnO 2 to crystalline Mn 2 O 3 and promoted the chemisorption of oxygen on the surface of MnO x -CeO x structures. Based on the data, a synergetic mechanism model of the deNO x activity is proposed for the MnO x -CeO x catalysts.