Hierarchical Structured Silver–Alumina Catalysts for Selective Catalytic Reduction of NO <i> _x </i> by Ethanol (EtOH‐SCR‐DeNO <i> _x </i> )

Abstract A hierarchically structured silver–alumina catalyst (Ag/AO‐SG) prepared by impregnation of meso‐/macroporous sol‐gel alumina was characterized by various temperature‐programmed methods and studied for selective catalytic reduction of NO x in the presence of ethanol (EtOH‐SCR‐DeNO x ). NH 3 ‐TPD and H 2 O‐TPD results indicated that the meso‐/macroporous Ag/AO‐SG catalysts possess a higher acidity and improved capacity for water adsorption. The EtOH‐SCR‐DeNO x experiments exhibited that the Ag/AO‐SG catalyst possesses a persistently high activity and selectivity in a temperature range between 220 and 330 °C. In contrast, the Ag/AO‐C catalyst (based on commercial mesoporous γ‐alumina) causes undesirable ethanol oxidation and is subjected to deactivation in the long‐term run below 300 °C. The TPO, TG, FTIR, and MS analyses showed that the deposit on the deactivated catalyst consists of melamine. Investigations on the effect of particle size on the EtOH‐SCR‐DeNO x reaction indicated the presence of internal diffusion limitations for the mesoporous Ag/AO‐C catalyst. Possible reaction pathways for the catalyst deactivation during EtOH‐SCR‐DeNO x are proposed.