Pt-Cu/SiO2 catalysts with different structures and chemical compositions were prepared using a two-step method. For the series of PtxCu100-x/SiO2 catalysts, Pt was deposited in the first step with H-2 PtCl6 as the precursor and Cu was deposited subsequently with Cu(NH3)(4)(2+) as the precursor. For the Cu100-xPtx/SiO2 catalyst, the deposition sequence was reversed accompanied with galvanic displacement of Cu-0 by Pt4+. All the samples were characterized by XRD, TEM, H-2-TPR, H-2 chemisorption. and DRIFT of CO adsorption, and evaluated for the catalytic hydrodechlorination of 1,2-dichloroethane. The results show that the PtxCu100-x/SiO2 catalysts exhibit core-shell structures with Pt-rich alloy cores and Cu-rich alloy shells, while the Cu100-xPtx/SiO2 catalyst shows a Pt-Cu alloy core and a Pt rich alloy shell. Different structures and chemical compositions lead to quite different performances in catalyzing the hydrodechlorination of 1,2-dichloroethane. The Pt16Cu84/SiO2 catalyst gave a high selectivity to ethylene over 90% and an excellent stability over 18 h run due to the Cu-rich shell structure, while the Cu44Pt56/SiO2 catalyst produced predominantly ethane due to the Pt rich shell. (c) 2012 Elsevier B.V. All rights reserved.