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

Ag and Pt-Ag catalysts supported on Al2O3-tungsten oxides (WOx) deposited on cordierite monoliths were prepared for the removal of nitrogen oxides (NOx) from diesel engine ex-haust emissions using C3H8 as well as H2 as reductants in the selective catalytic reduction. The catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), tempera-ture programmed reduction (TPR), scanning electron microscopy (SEM/EDX), transmis-sion electron microscopy (STEM/HAADF), H2 chemisorption, and Raman and UV-vis spectroscopy of the evaluated catalysts. The conversion of NO, C3H8 and CO was studied as a function of three GHSVs 30,000, 70,000 and 100,000 h-1 as well as the reaction tem-perature. The combination of 0.1wt%Pt-2wt%Ag /Al₂O₃-WOx on cordierite monoliths was active in NO reduction and CO and C₃H8 combustion. By STEM, small Pt-Ag bimetallic particles (20 nm) presented a high Pt concentration (58.6 atom%). Separate Ag particles were also detected. The best preparation conditions of boehmite AlO(OH)/cordierite mon-olith were obtained by applying three or four boehmite AlO(OH) impregnations, drying, calcination in air flow, and H₂ reduction at 500 °C and exchange with H₂PtCl₃ and AgNO3. A one-dimensional model of NO conversion as a function of reactor length was proposed considering external mass transfer limitations as dominant.