A catalyst obtainable by exsolving particles of Ni, Co and/or a mixture of Ni and Co from a perovskite metal oxide of formula (I) (M1aM2b)(COxNiyM3z)O3, wherein M1 and M2 are each independently an alkali earth metal or a rare earth metal, M3 is Ti or Cr, 0≤a≤1, 0≤b≤1, 0 0. The invention includes methods of converting this catalyst into one or more catalytically active forms. The catalysts and the activated forms of same are useful in the catalysing CO oxidation and/or NO oxidation.