Bimetallic Pt-Cu catalyst precursors have been prepared from NO^3--Mg/Al layered double hydroxide (LDH) by anionic exchange with negatively charged copper hydroxy citrate colloids ([Cu(C₆O₇H₃)_x(OH)]_y^{y(3x- 1)-)} and [PtCl₆]^2- species. Successive exchanges by varying the addition order of the two anionic species allowed removing NO^3- almost completely and obtaining Cu/Pt molar ratios of 50.2 and 6.8 when Cu-containing colloids were introduced first (CuPt) or second (PtCu), respectively. After calcination and reduction treatments, the resulting materials were characterized by TPR and XPS analyses. Pt and Cu particles were homogeneously dispersed with the particle size of 2-7 nm and the portion of Cu present as Pt-Cu alloy was 48.9% (CuPt) and 69.8% (PtCu), showing remarkably enhanced alloy formation by the PtCu exchange order. Using this PtCu material, total conversion in nitrate hydrogenation reaction was achieved with higher selectivity toward nitrogen than those reported with bimetallic Pd-Cu catalysts prepared from LDH precursors by impregnation and co-precipitation routes.