In 1971, Jones et al. [12] pointed out that H2 can react preferentially with NO over O2 in the reaction system of H2–NO–O2 on commercially supported Pt catalysts, suggesting the possibility of H2-SCR, although the reaction was not performed in excess oxygen conditions. Lamb and Tollefson [13] also reported the catalytic reduction of NO with H2 in the presence of O2 in low concentration and high velocity gas streams. Probably the first report to confirm H2-SCR in net-oxidizing conditions is the one by Fu and Chuang [14]. They reported that stable NOx conversions of 60–80% were obtained at temperatures above 55 °C and at space velocities from 3000 to 10,000 h−l for a feed containing 1000 ppm NOx, 1% H2, and 3.2% O2 in N2 by using noble metal catalysts supported on styrene-di-vinylbenzene copolymer (SDB). The catalytic activity of the noble metals was found to be in the order of Pt > Pd–Ru > Pd > Ru ≫ Au. In this catalytic reaction, low reaction temperature was essential to the selective NO–H2 reaction due to the competitive reaction between H2 and O2, indicating the presence of a temperature window for H2-SCR. It was also reported that introduction of H2O did not affect the reaction because of the hydrophobic support material. In 1994, Wildermann [15] showed that a Pt–Mo catalyst supported on Al2O3 is active for the selective NO–H2 reaction in the presence of 8% O2. It was confirmed that Pt is the most active for H2-SCR among noble metals, although undesirable N2O formation is considerable in addition to N2 as a reduction product of NO.