Selective Catalytic Reduction of NO with H2 over Pt/Pd-Containing Catalysts on Silica-Based Supports

Platinum- and/or palladium-containing silica-based supports were applied for the selective catalytic reduction of NOx with hydrogen (H2-SCR-DeNOx). To obtain enhanced activity and N2 selectivity below 150 °C, we varied the type and loading of noble metals (Pt and Pd both individually and paired, 0.1–1.0 wt.-%), silica-containing supports (ZrO2/SiO2, ZrO2/SiO2/Al2O3, Al2O3/SiO2/TiO2), as well as the H2 concentration in the feed (2000–4000 ppm). All of these contributed to enhancing N2 selectivity during H2-SCR-DeNOx over the (0.5 wt.-%)Pt/Pd/ZrO2/SiO2 catalyst in the presence of 10 vol.-% of O2. H2 was completely consumed at 150 °C. A comparison of the catalytic results obtained during H2-SCR-DeNOx,(H2-)NH3-SCR-DeNOx, as well as stop-flow H2-SCR-DeNOx and temperature-programmed studies, revealed that in the temperature range between 150 and 250 °C, the continuously coupled or overlaying mechanism of NO reduction by hydrogen and ammonia based on NH3 formation at lower temperatures, which is temporarily stored at the acid sites of the support and desorbed in this temperature range, could be postulated.