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

•CoMn2O4 with excellent NH3-SCO activity was synthesized by modulating B site spinel.•CoMn2O4 achieved complete conversion of NH3 at 150 °C.•The superior redox property and formation of more oxygen vacancies promoted the activity.•The enhancement of N2 selectivity was due to the interaction of Co and Mn in CoMn2O4.•In situ DRIFTS indicated the presence of both i-SCR and hydrazine mechanism.