Mono and bimetallic Mn–Fe catalysts supported on different materials were prepared and their catalytic performance in the NH₃–SCR of NO_x was investigated. It was shown that Mn and Fe have a synergic effect that enhances the activity at low temperature. Nevertheless, the activity of the bimetallic catalysts depends very much on the support selected. The influence of the support on the catalyst activity has been studied using materials with different textural and acid–base properties. Microporous (BEA-zeolite), mesoporous (SBA15 and MCM41) and bulk (metallic oxides) materials with different acidity have been used as supports for the Mn–Fe catalysts. It has been shown that the activity depends on the acidity of the support and on the surface area. Acid sites are necessary for ammonia adsorption and high surface area produces a better dispersion of the active sites resulting in improved redox properties. The best results have been obtained with the catalysts supported on alumina and on beta zeolite. The first one is the most active at low temperatures but it presents some reversible deactivation in the presence of water. The Mn–Fe catalyst supported on beta zeolite is the most active at temperatures higher than 350 °C, without any deactivation in the presence of water and with a 100% selectivity towards nitrogen.