Enhanced NH3-SCR performance of high-silica MER zeolite via template synthesis

Abstract

Amid increasingly stringent regulations on NOx emissions from diesel vehicles, Cu-based zeolite catalysts for ammonia selective catalytic reduction (NH₃-SCR) are considered among the most effective solutions. MER zeolite, featuring a three-dimensional (3D) topology with 8-membered ring (8 MR) micropores, is typically Al-rich (Si/Al < 3) in conventional template-free synthesis. In this study, hierarchical O-MER zeolite with a higher Si/Al ratio (6.01) was efficiently synthesized using N, N-1, 1, 2, 6-tetramethylpiperidine as an organic template via inter-zeolite conversion over a crystallization period of 7–72 h. Compared to C-MER zeolite synthesized template-free, the Cu-based MER zeolite exhibited significantly enhanced NH₃-SCR catalytic performance, achieving over 90 % NOx conversion within the 220–550 °C range for the fresh sample. Even after hydrothermal aging at 750 °C for 16 h, the sample maintained over 80 % NOx conversion between 250 and 550 °C. Comprehensive characterization revealed that hydrothermal aging partially degraded the crystalline structure of O-MER zeolite, notably reducing the number of acid sites, particularly Z-[Cu²⁺(OH)⁻]⁺, which decreased NO activation and storage, thereby impacting low-temperature activity. The sustainable synthesis of MER zeolite and its robust catalytic performance present promising candidates for the future development of efficient and cost-effective SCR catalysts.