A comprehensive study has been performed on the catalytic properties of composite catalysts [Mn/support + FeBeta] and their individual components (Mn/support and FeBeta) in the selective catalytic reduction of nitrogen oxides and the ammonia oxidation reaction. It has been shown that mixing the oxide component with the zeolite not only leads to an increase in NO (x) conversion, but also improves the selectivity in the oxidation of residual ammonia, thus making it possible to conduct both processes in a single catalytic unit.