Synergistic Effect of Cu/CeO2 and Pt-BaO/CeO2 Catalysts for a Low-Temperature Lean NO x Trap.

A lean NO x trap (LNT) catalyst has been widely used for removing NO x exhaust from lean-burn engines. However, the operation range of LNT has been limited because of the poor activity of LNT catalysts at low temperatures (≤300 °C), especially in urban driving conditions. To increase NO x removal efficiency during lean-rich cycle operation, a Cu/CeO2 (CC) catalyst was added to a Pt-BaO/CeO2 (PBC) catalyst. In comparison to PBC- or CC-only catalysts, the physical mixture of PBC and CC catalysts (PBC + CC) exhibited a significant synergy for both NO x storage and reduction efficiencies. In particular, low-temperature activity below 200 °C was greatly enhanced. A Pt-BaO-Cu/CeO2 (PBCC) catalyst, which was synthesized by depositing Pt and Cu together on a ceria support, showed poorer NO x removal efficiency. The origin of the synergistic effect over PBC + CC was investigated. Under lean conditions, the CC showed much better activity for NO oxidation, allowing for faster NO x storage on PBC. Under rich conditions, H2 was generated in situ on the CC by a water-gas shift reaction then accelerated the reduction of NO x, which had been stored on PBC, with a higher selectivity to N2. This simple modification in the catalyst can provide an important clue to enhance low-temperature activity of the commercial LNT system.

Fully Copper-Exchanged High-Silica LTA Zeolites as Unrivaled Hydrothermally Stable NH3 -SCR Catalysts.

Diesel engine technology is still the most effective solution to meet tighter CO2 regulations in the mobility and transport sector. In implementation of fuel-efficient diesel engines, the poor thermal durability of lean nitrogen oxides (NOx ) aftertreatment systems remains as one major technical hurdle. Divalent copper ions when fully exchanged into high-silica LTA zeolites are demonstrated to exhibit excellent activity maintenance for NOx reduction with NH3 under vehicle simulated conditions even after hydrothermal aging at 900 °C, a critical temperature that the current commercial Cu-SSZ-13 catalyst cannot overcome owing to thermal deactivation. Detailed structural characterizations confirm the presence of Cu2+ ions only at the center of single 6-rings that act not only as a catalytically active center, but also as a dealumination suppressor. The overall results render the copper-exchanged LTA zeolite attractive as a viable substitute for Cu-SSZ-13.