Influence of Supports on Pd Catalysts for the Selective Catalytic Reduction of NO_x with H_2 and CO

摘要

A major concern of current commercial catalysts for the selective catalytic reduction (SCR) of nitrogen oxides (NO_x) (DeNO_x) is the lack of sufficient catalytic activity at low temperatures (below 200℃) that typically occur during cold start and urban driving conditions. To address this issue, a study was undertaken to develop an (H_2 + CO)-SCR Pd-based catalyst to obtain high DeNO_x activity in this low-temperature range. A series of catalysts with Pd loaded on supports containing various amounts of γ-alumina (γ-Al_2O_3) (0-65 wt%), CBV-2314 (15-100 wt%), and TiO_2 (0-20 wt%) were tested for DeNO_x activity and aging in a catalyst testing unit (CTU). The results showed that each component in the support played a role in the NO_x conversion, depending on the temperature. Catalysts with Pd supported on {[γ-Al_2O_3 (60 wt%)+CBV-2314 (20 wt%)]-TiO_2 (20 wt%)} achieved the best overall DeNO_x activity. Catalysts with various Pd loadings (0.05 wt% to 0.5 wt%) were prepared with a {[γ-Al_2O_3 (60 wt%)+CBV-2314 (20 wt%)]-TiO_2 (20 wt%)} support. The catalysts loaded with 0.05 wt% and 0.2 wt% Pd demonstrated the best overall DeNO_x activity (up to 90 % NO_x conversion starting at 150 ℃). These catalysts were subjected to an accelerated aging regime. Based on the aging studies, the 0.2 wt% Pd/{[γ-Al_2O_3 (60 wt%)+CBV-2314 (20 wt%)]-TiO_2 (20 wt%)} composition was the most active and stable catalyst.