Study on the pyrolysis of ammonium thiocyanate and its product formation characteristics in H2

•Waste heat of coking oven gas pyrolyze highly NH4SCN-containing waste water.•The participation of H2 reduced the pyrolysis end temperature of NH4SCN by 120 °C.•The gaseous products of NH4SCN in H2 are HNCS, NH3, CS2 and H2S.•Thiourea, guanidine, cyanamide and its polymers are considered as intermediates.•Final product can be collected is graphitic carbon nitride (g-C3N4).