Catalytic oxidation of ammonia: A pre-occupied-anchoring-site strategy for enlarging Ag nanoparticles at low Ag loading and achieving enhanced activity and selectivity on Ag-CuOx/Al2O3 catalyst.

The Ag nanoparticles (Ag NPs) in Ag/Al 2 O 3 catalysts play a crucial role in the selective catalytic oxidation of NH 3 (NH 3 -SCO). To enhance NH 3 -SCO activity, Cu, which has stronger anchoring ability than Ag, is introduced onto Al 2 O 3 , reducing available anchoring sites for Ag. As Ag cannot displace anchored Cu species, Ag species agglomerate into larger Ag NPs even with low Ag loading. Consequently, these enlarged Ag NPs become more active centers for NH 3 -SCO. The optimal Ag:Cu molar ratio is confirmed as 2:3. This 'pre-occupied-anchoring-site' strategy decreases Ag loading to 1/5 of the original, reducing catalyst costs while maintaining activity. In situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) studies reveal that NH 3 -SCO on 2Ag1.8Cu/Al (weight ratio) catalyst follows the hydrazine mechanism below 200 °C, coexisting with the imide mechanism from 200–250 °C, and solely the imide mechanism beyond 250 °C. This strategy is applicable to various transition metals, including Mn, Co, Ni, and Fe, promoting cost-effective Ag NPs formation. [Display omitted] • Pre-occupied-anchoring-site strategy is proposed based on metal anchoring strength. • This strategy can promote the agglomeration of low-loading Ag into nanoparticles. • This strategy can reduce catalyst cost and improve the NH 3 -SCO performance. • The anchoring mechanism of pre-occupied-anchoring-site strategy is universal. [ABSTRACT FROM AUTHOR]