The catalytic NO-H-2-O, reaction at low temperatures (50-130 degrees C) has been investigated over Pt-supported Mg-Al binary oxides, which were prepared from PtCl62- and Pt(NO2)(4)(2-)-exchanged hydrotalcite(HT)-like compounds by heating at 600 degrees C in H,. Although the NO, conversion of both catalysts was similarly high (> 80%) at around 70 degrees C, the Pt(NO2)(4)(2-)-HT catalyst exhibited the higher selectivity to N-2 (53% N-2 and 47% N2O), compared to 12% N-2 and 88% N2O for the PtCl6(2-)-HT catalyst. The XANES/EXAFS spectroscopy showed that Pt prepared from PtC1(6)(2-)-HT is partly oxidized due to the coordination of residual chlorides, whereas Pt(NO2)(4)(2-) -HT yielded highly dispersed metallic Pt. Because of the presence of chloride strongly bound to Pt, the oxidative NO adsorption as NO2/NO3 was inhibited for PtCl62--HT. The improved N2 selectivity with an increase of oxidative NO adsorption is in accord with the catalytic property of Na-Pt/ZSM-5 in our previous work [M. Machida, T. Watanabe, Appl. Catal. B: Environ. 52 (2004) 281.1, suggesting that the N-2 would be formed via NO2/NO3 intermediates. (c) 2006 Elsevier B.V. All rights reserved.