The effect of chloride in Pd precursors on catalyst activity and stability of Pd-Ni/Y2O3 catalyst was investigated for oxy-CO2 reforming of methane. A series of Pd-Ni/Y2O3 catalysts with different Pd precursors (PdCl2 and Pd(NO3)(2)) was prepared using wet-impregnation method over Y2O3 support. The presence of chloride in the Pd(Cl)-Ni/Y2O3 catalyst (PdCl2 as precursor) aids in formation of Pd-Y2O3 compound which can interact with Ni to form bilayer Pd-Ni and prevent agglomeration at high temperature reaction condition. The presence of Pd-Y2O3 compound is of very importance for superior catalytic stability of Pd(Cl)-Ni/Y2O3 catalyst. The catalytic activity of Pd(Cl)-Ni/Y2O3 catalyst is much better than Pd(N)Ni/Y2O3 catalyst (Pd(NO3)(2) as precursor) due to smaller metal particle size and synergy between Pd and Ni to form bimetallic particles on the Pd(CI)-Ni/Y2O3 catalyst. The effect of metal particle size on catalytic activities is clearly shown in Pd(C)-Ni/Y2O3 catalyst with various Pd/Ni ratios. A formation mechanism of bilayer Pd-Ni formed by interfacial chloride is proposed for Pd(Cl)-Ni/Y2O3 catalyst. (C) 2016 Elsevier B.V. All rights reserved.