Influence of Supports on Pd Catalysts for the Selective Catalytic Reduction of NOx with H2 and CO

Abstract

A major concern of current commercial catalysts for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) (DeNOx) is the lack of sufficient catalytic activity at low temperatures (below 200°C) that typically occur during cold start and urban driving conditions. To address this issue, a study was undertaken to develop an (H2 + CO)-SCR Pd-based catalyst to obtain high DeNOx activity in this low-temperature range. A series of catalysts with Pd loaded on supports containing various amounts of γ-alumina (γ-Al2O3) (0–65 wt%), CBV-2314 (15–100 wt%), and TiO2 (0–20 wt%) were tested for DeNOx activity and aging in a catalyst testing unit (CTU). The results showed that each component in the support played a role in the NOx conversion, depending on the temperature. Catalysts with Pd supported on {[γ-Al2O3 (60 wt%) + CBV-2314 (20 wt%)]–TiO2 (20 wt%)} achieved the best overall DeNOx activity. Catalysts with various Pd loadings (0.05 wt% to 0.5 wt%) were prepared with a {[γ-Al2O3 (60 wt%) + CBV-2314 (20 wt%)] − TiO2 (20 wt%)} support. The catalysts loaded with 0.05 wt% and 0.2 wt% Pd demonstrated the best overall DeNOx activity (up to 90 % NOx conversion starting at 150 °C). These catalysts were subjected to an accelerated aging regime. Based on the aging studies, the 0.2 wt% Pd / {[γ-Al2O3 (60 wt%) + CBV-2314 (20 wt%)] − TiO2 (20 wt%)} composition was the most active and stable catalyst.