Classify the following room-temperature reactions as homogenous catalysis or heterogeneous catalysis:
a. reaction of carbon monoxide and oxygen in a presence of platinum
b. reaction of sulfur dioxide and oxygen over vanadium oxide
c. synthesis of ammonia gas from nitrogen and hydrogen in a presence of potassium oxide
d. reaction of persulfate ions and iodide ions in water in presence of iron (II) ions
e. reaction of 2,3-dihydroxybutanedioate ions and hydrogen peroxide in presence of cobalt (II) ions