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

Ammonia (NH3) 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/Al2O3 catalysts with different Al2O3 particle sizes (micro-Al2O3 and nano-Al2O3) were prepared and tested for the selective catalytic oxidation of ammonia (NH3-SCO). It was shown that Ag/nano-Al2O3 was much more active than Ag/micro-Al2O3 for NH3-SCO in the low-temperature range. The results of characterization by BET, TEM, NH3-TPD, XRD, H-2-TPR, UV vis, and XAFS revealed that Ag/nano-Al2O3 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 NH3, therefore resulting in much higher NH3-SCO activity. In addition, on the basis of in situ DRIFTS, kinetic measurements, and DFT calculation results, we discovered that the NH3-SCO reaction over Ag/nano-Al2O3 follows a reaction pathway we call the N-2(-) mechanism.