The insight into reaction mechanism of diethylamine catalytic abatement over various Cu-based catalysts

Abstract

This work investigated the reaction behaviors of diethylamine (DEA) catalytic oxidation on various Cu-based catalysts with different supports (TiO2, HZSM-5(27), HZSM-5(130) and S-1). It was found that the acidic environment of catalysts greatly influenced reaction pathways of DEA oxidation. On Cu5/TiO2 catalyst mainly with Lewis acidity, DEA preferentially dissociated through a two-step dehydrogenation to produce acetonitrile and ethylene, while on Cu5/HZSM-5(27) catalyst with strong Brønsted acidity, DEA could directly decompose into ethylamine and ethylene via N-C cleavage. Both pathways existed simultaneously over Cu5/HZSM-5(130) with decreased Brønsted acidity. Thereafter, acetonitrile could be further oxidized on the Cu5/TiO2 catalyst to generate a large amount of NOx via NCO(a) intermediates over-oxidation, while ethylamine on Cu5/HZSM-5 samples would convert to acetamide and then produced N2 and CO2. The Cu2+ species due to enriched Brønsted acid sites in Cu5/HZSM-5 catalysts ensured excellent N2 selectivity via internal SCR mechanism. Additionally, the strong Brønsted acidity of Cu5/HZSM-5(27) could induce the polymerization of carbonaceous intermediates and thereby resulted in severe coke deposition. As for Cu5/HZSM-5(130) and Cu5/S-1 with relatively lower Brønsted acidity and reducibility would release some unwanted gas-phase by-products like ethyl-isocyanate. This work provided useful guidance for designing NVOCs catalysts with high activity and less toxic by-products.