One-pot hydrothermal synthesis of dual metal incorporated CuCe-SAPO-34 zeolite for enhancing ammonia selective catalytic reduction

Abstract

A series of dual metal incorporated CuCex-SAPO-34(x = 0–0.04) samples were synthesized using one-pot hydrothermal method with diethylamine as organic structure-directing agent for selective catalytic reduction of NOx by NH3. The catalytic properties were elucidated in detail with physicochemical properties being analyzed using various instruments. All the catalysts exhibited typical SAPO-34 crystal structures with high specific surface areas. With the dual-metal incorporation, the surface acidity and amount of isolated Cu2+, which may be active sites for NH3-SCR, were significantly enhanced. However, excessive Ce restrained the formation of isolated Cu2+ due to its occupation of cationic sites. Therefore, the 0.05CuCe0.02-SAPO-34 exhibited high NO conversion (≥80%) at 168°C-500°C. Furthermore, the NH3-SCR mechanism over different catalysts was investigated in-situ DRIFTS experiments. For the 0.05Cu-SAPO-34, the adsorbed NH3 species react with gaseous NO and following the E-R mechanism throughout the reaction temperature range. Meanwhile, adsorbed NO2 was detected and reacted with the adsorbed NH3 species according to the L-H mechanism in low-temperature region. In contrast, the NH3-SCR reaction over the 0.05CuCe0.02-SAPO-34 primarily followed the E-R mechanism throughout the temperature range. The L-H mechanism was cut off due to the loss of the adsorption ability of nitrous species at high temperatures., resulting in NO conversion decreasing.