Rational tuning towards B-sites (B = Mn, Co, Al) on CoB2O4 binary oxide for efficient selective catalytic oxidation of ammonia

• CoMn 2 O 4 with excellent NH 3 -SCO activity was synthesized by modulating B site spinel. • CoMn 2 O 4 achieved complete conversion of NH 3 at 150°C. • The superior redox property and formation of more oxygen vacancies promoted the activity. • The enhancement of N 2 selectivity was due to the interaction of Co and Mn in CoMn 2 O 4 . • In situ DRIFTS indicated the presence of both i-SCR and hydrazine mechanism. NH 3 catalytic oxidation technology (NH 3 -SCO) is promising for the direct conversion of NH 3 to N 2 and H 2 O. Currently, balancing its NH 3 catalytic oxidation activity and N 2 selectivity remains a challenge. Herein, the redox properties and the surface oxygen vacancies of CoB 2 O 4 were modulated to enhance the activity of the catalyst by using three elements (Co, Mn, Al) as the B-site elements of the CoB 2 O 4 spinel. Eventually, CoMn 2 O 4 synthesized with Mn as the B-site element possessed more surface oxygen vacancies and generated Mn 3+ -Mn 4+ pairs that could facilitate the redox properties compared with CoAl 2 O 4 and CoCo 2 O 4 due to the interaction between Co and Mn, which in turn enhanced its catalytic activity together and enabled the complete conversion of NH 3 at 150°C. Additionally, using Mn as the B-site element of CoB 2 O 4 also facilitated the generation of the Bronsted acid sites on the catalyst surface, which was beneficial to its N 2 selectivity (65% at 150°C). In situ DRIFTs indicated the existence of two reaction mechanisms over CoMn 2 O 4 : the i-SCR mechanism with bidentate nitrate as the primary reactive intermediate species and the hydrazine mechanisms with -NH 2 and N 2 H 4 as the main intermediate species.