The selective catalytic reduction (SCR) of NO, by H-2 was studied using proton-conducting Sn0.9In0.1 P2O7 as a catalyst support at 50-350 degrees C. When a mixture of 800 ppm NO, 1400-8400 ppm H2, and 5% 02 in Ar was introduced to the Pt/C working electrode, NO, was reduced to N-2 with N2 selectivity values >80%. The reaction mechanism was shown to be based on a mixed potential at the Pt/C working electrode. This mechanism was also applicable to a Sn0.9In0.1 P2O7-supported Pt catalyst. H2 SCR over the Pt/Sn0.9In0.1 P2O7 catalyst was characterized by a wide operating temperature window (50-350 degrees C) and remarkable N2 selectivity values (>80%). Catalyst performance could be further improved by the addition of Rh to Pt, in which NO, conversion was a maximum 1.4 times higher than that over the Pt/Sn0.9In0.1 P2O7 catalyst and N-2 selectivity was increased to >89% at all temperatures tested. (C) 2007 Elsevier Inc. All rights reserved.