Mechanism of Zn salt-induced deactivation of a Cu/activated carbon catalyst for low-temperature denitration via CO-SCR

Catalytic removal of gaseous pollutant NO using CO: Catalyst structure and reaction mechanism

Carbon monoxide (CO) has recently been considered an ideal reducing agent to replace NH3 in selective catalytic reduction of NOx (NH3-SCR). This shift is particularly relevant in diesel engines, coal-fired industry, the iron and steel industry, of which generate substantial amounts of CO due to incomplete combustion. Developing high-performance catalysts remain a critical challenge for commercializing this technology. The active sites on catalyst surface play a crucial role in the various microscopic reaction steps of this reaction. This work provides a comprehensive overview and insights into the reaction mechanism of active sites on transition metal- and noble metal-based catalysts, including the types of intermediates and active sites, as well as the conversion mechanism of active molecules or atoms. In addition, the effects of factors such as O2, SO2, and alkali metals, on NO reduction by CO were discussed, and the prospects for catalyst design are proposed. It is hoped to provide theoretical guidance for the rational design of efficient CO selective catalytic denitration materials based on the structure-activity relations.

Rationally tailored redox ability of Sn/γ-Al2O3 with Ag for enhancing the selective catalytic reduction of NO x with propene

The development of excellent selective catalytic reduction (SCR) catalysts with hydrocarbons for lean-burn diesel engines is of great significance, and a range of novel catalysts loaded with Sn and Ag were studied in this work. It was found that the synergistic effects of Sn and Ag enabled the 1Sn5Ag/γ-Al₂O₃ (1 wt% Sn and 5wt% Ag) to exhibit superior C₃H₆-SCR performance. The de-NO _x efficiency was maintained above 80% between 336 and 448 °C. The characterization results showed that the presence of AgCl crystallites in the 1Sn5Ag/γ-Al₂O₃ catalyst helped its redox ability maintain an appropriate level, which suppressed the over-oxidation of C₃H₆. Besides, the number of surface adsorbed oxygen (O_α) and hydroxyl groups (O_γ) were enriched, and their reactivity was greatly enhanced due to the coexistence of Ag and Sn. The ratio of Ag⁰/Ag⁺ was increased to 3.68 due to the electron transfer effects, much higher than that of Ag/γ-Al₂O₃ (2.15). Lewis acid sites dominated the C₃H₆-SCR reaction over the 1Sn5Ag/γ-Al₂O₃ catalyst. The synergistic effects of Sn and Ag facilitated the formation of intermediates such as acetates, enolic species, and nitrates, and inhibited the deep oxidation of C₃H₆ into CO₂, and the C₃H₆-SCR mechanism was carefully proposed.