A Co-Mn/Ni foam catalyst and alkali metal K-poisoned catalyst were prepared by an impregnation method using foamed Ni metal as a carrier. Mn was the active component, and Co was a trace auxiliary. The effects of different levels of alkali metal K poisoning and different concentrations of Co auxiliaries on the K poisoning resistance of the catalyst were studied. The results showed that the number of Bronsted acid sites on the surface of the catalyst, the reduction capacity and the number of unsaturated Ni atoms decreased after the addition of K. The interaction between the active Mn and the metallic Ni decreased, and the activity of the catalyst decreased. As the addition amount of added K increased, the catalyst alkali metal poisoning phenomenon became more significant. The kinetic studies showed that the activation energy increased after the addition of K, whereas the activation energy of K0.3Co0.5/Fresh catalyst decreased after Co modification. The amounts of Bronsted acid and Lewis acid sites on the surface of the K-poisoned catalyst were improved dramatically by Co modification of the Mn/Ni foam catalyst. K destroys the extremely important Bronsted acid sites that adsorb and activate NH3, reducing the performance to less than half. Additionally, NH3-TPD and in situ DRIFT analyses showed that Co, K, Mn and Ni synergistically improved the acid sites. The number of Bronsted acid sites and Lewis acid sites on the catalyst surface were greatly increased in the K0.3Co0.5/Fresh catalyst, whose reduction performance increased substantially compared with the K-0.3/Fresh catalyst.