Inhibition discrimination of different chloride salts on coal functional groups

•A new Quantitative approach to weight its compositions changes by analyzed functional groups content percentage and to determine its reactivity ranking by analyzed functional groups activation rate.•The chain thermal reaction of ten active groups were analyzed to reveal the oxidation mechanism of functional groups in coal combustion spontaneous.•The inhibition reaction of magnesium chloride on coal samples was different from those of sodium chloride and potassium chloride, which led to the different temperature stages in which the blocking effect occurs.•The inhibition effect of sodium chloride and potassium chloride was mainly manifested in the two-stage involving dehydration/desorption and dynamic equilibrium (below T3).•The inhibition effect of magnesium chloride presents in the whole coal-oxygen reaction.