θ-Al2O3/FeO1.25 possessing a special ring complex of FeII---HO===FeIII for the efficient catalytic semi-hydrogenation of acetylene under front–end conditions

•Firstly using metal oxide as catalyst for the semi-hydrogenation of acetylene.•High conversion of acetylene and ethylene selectivity under front–end conditions.•Constructing a special ring complex of FeIII, FeII and hydroxyl groups.•Excellent activity and stability on a 750 mL industrial side-line device.•θ-Al2O3/FeO1.25-6%-500-450 were prepared by an industrially feasible strategy.