Selective hydrogenolysis of biomass-derived glycerol to 1,2-propanediol (1,2-PDO) is a significant reaction for the production of high value-added chemicals, in which design and preparation of high-performance heterogeneous catalysts remain a big challenge. Herein, we report a PtIn alloy catalyst with a tunable electronic and geometric structure, confirmed by several elaborate characterizations including high-resolution transmission electron microscopy, in situ CO-DRIFTS, quasi in situ X-ray photoelectron spectroscopy, and in situ X-ray absorption fine structure (XAFS) analysis. As expected, the PtIn2 catalyst exhibits remarkably enhanced catalytic behavior for glycerol hydrogenolysis to 1,2-PDO (conversion: 99.8%; selectivity: 91.1%) with a turnover frequency value of 222 h(-1), much larger than that of a pristine Pt catalyst and among the highest level of those of the reported Pt-based catalysts under mild reaction conditions (200 degrees C, 2.0 MPa). Furthermore, both in situ studies (in situ glycerol-XAFS and in situ glycerol-DRIFTS) and catalytic evaluations verify that the Ptln alloy structure contributes to the dramatically improved catalytic performance: the Pt delta- site at the Pt-In alloy interface serving as the intrinsic catalytic active center improves the activation and breakage of alpha-C-H and bonded hydroxyl groups in glycerol molecules, while the discrete Pt sites suppress the C-C bond cleavage. Consequently, the alloying effect changes the catalytic active center and promotes the rate-determining step (the formation of intermediate glyceraldehyde) in contrast to the traditional monometallic Pt catalyst. Our study demonstrates a successful paradigm in the design of highly efficient Pt-based catalysts by virtue of alloying, which would inspire more explorations on other noble metal systems.