Ag-Pt/Al2O3-WOx Catalysts Supported on Cordierite Honeycomb for the Reduction of NO with C3H8, CO, and H2

Selective catalytic reduction (SCR) of NO using various reducing agents is a critical area of research for mitigating environmental pollution. In this study, the influence of active phase loading was investigated in four bimetallic Pt-Ag/Al2O3-WOx catalysts, one monometallic Ag/Al2O3-WOx catalyst, and one Pt-Ag/Al2O3-WOx catalyst subjected to high-severity air-SO2 pretreatment. All catalysts were supported on cordierite monoliths, and their performance in NO SCR was evaluated using H2, C3H8, and CO as reducing agents. An increase in the active phase loading (Pt-Ag/Al2O3) from 10.7 wt% to 17.4 wt% resulted in higher conversions of NO, C3H8, and H2, as well as improved N2 selectivity. However, CO conversion decreased as the active phase loading increased, which was attributed to competitive reduction by H2, since both reactions occur within the same temperature range (100–200 °C). The presence of N2O below 6 ppm was observed in some catalysts. Furthermore, higher active phase loadings led to increased carbon deposition; the Ag/Al2O3-WOx catalyst exhibited the highest carbon content (5 wt%). The deposited carbon was identified as ordered graphitic carbon. In the Pt-Ag catalysts, the presence of Ag+ and Agⁿδ+ species, as well as the Ag° plasmon, was identified by UV-Vis spectroscopy. STEM analysis showed Ag-Pt crystallites with an average size of 24 nm, which may have contributed to the higher NO conversion observed at 350 °C and the improved N2 selectivity at 100 °C in the Pt-Ag bimetal catalysts, compared to the activity of the Ag/Al2O3-WOx catalyst.