Improved NOx Reduction Using C3H8 and H2 with Ag/Al2O3 Catalysts Promoted with Pt and WOx

Abstract

The addition of Pt (0.1 wt%Pt) to the 2 wt%Ag/Al2O3-WOx catalyst improved the C3H8– Selective Catalytic Reduction (SCR) of NO assisted by H2 and widened the range of the operation window. During H2–C3H8–SCR of NO, the bimetallic Pt–Ag catalyst showed two maxima in conversion: 80% (at 130 °C) and 91% (between 260 and 350 °C). This PtAg bimetallic catalyst showed that it could combine the catalytic properties of Pt at low temperature, with the properties of Ag/Al2O3 at high temperature. These PtAg catalysts were composed of Ag+, Agnδ+ clusters, and PtAg nanoparticles. The catalysts were characterized by Temperature Programmed Reduction (TPR), Ultraviolet Visible Spectroscopy (UV-Vis), Scanning Electron Microscopy (SEM)/ Energy Dispersed X-ray Spectroscopy (EDS), x-ray Diffraction (XRD) and N2 physisorption. The PtAg bimetallic catalysts were able to chemisorb H2. The dispersion of Pt in the bimetallic catalysts was the largest for the catalyst with the lowest Pt/Ag atomic ratio. Through SEM, mainly spherical clusters smaller than 10 nm were observed in the PtAg catalyst. There were about 32% of particles with size equal or below 10 nm. The PtAg bimetallic catalysts produced NO2 in the intermediate temperature range as well as some N2O. The yield to N2O was proportional to the Pt/Ag atomic ratio and reached 8.5% N2O. WOx stabilizes Al2O3 at temperatures ≥650 °C, and also stabilizes Pt when it is reduced in H2 at high temperature (800 °C).