Nanosize Effect of Al₂O₃ in Ag/Al₂O₃ Catalyst for the Selective Catalytic Oxidation of Ammonia

Ammonia (NH 3 ) has potentially harmful effects on human health and has recently been found to be an important factor in the formation of haze; thus, its emission control is urgent, especially during haze pollution periods. In this work, two kinds of Ag/Al 2 O 3 catalysts with different Al 2 O 3 particle sizes (micro-Al 2 O 3 and nano-Al 2 O 3 ) were prepared and tested for the selective catalytic oxidation of ammonia (NH 3 -SCO). It was shown that Ag/nano-Al 2 O 3 was much more active than Ag/micro-Al 2 O 3 for NH 3 -SCO in the low-temperature range. The results of characterization by BET, TEM, NH 3 -TPD, XRD, H 2 -TPR, UV–vis, and XAFS revealed that Ag/nano-Al 2 O 3 possesses much smaller Ag particles and more metallic Ag species (Ag NPs ) and also contains abundant acid sites, which facilitate the adsorption and dissociation of NH 3, therefore resulting in much higher NH 3 -SCO activity. In addition, on the basis of in situ DRIFTS, kinetic measurements, and DFT calculation results, we discovered that the NH 3 -SCO reaction over Ag/nano-Al 2 O 3 follows a reaction pathway we call the N 2 – mechanism.