The manufacturing of ultrathin Pd based hydrogen separation membranes with high permeation performance has great potential in industrial applications. However, there usually exists a trade-off between reduced thickness and high hydrogen permselectivity which are regarded as a pair of contradictory requirements. In this study, a novel technique of confined and in-situ zeolite synthesis for defects reparation is proposed to improve the hydrogen permselectivity of preformed Pd membranes without further increasing their thickness. Two technology routes are developed for different defect dimensions. Zeolites can only grow inside large defects in one route, which is suitable for repairing broken membranes. In the other route, a thin zeolite layer is formed on Pd membrane surface, covering small defects for further enhancing selectivity. The purity of permeate hydrogen is enhanced from 99.884 to 99.994% after zeolite reparation. High purity hydrogen (99.986%) can be separated from 75% H-2/N-2 mixture with a hydrogen recovery of 91% by the repaired membrane at 500 degrees C and 0.4 MPa. (C) 2017 Elsevier B.V. All rights reserved.