The CombiNO(x) process includes a family of NOx control technologies (reburning, urea injection, methanol injection, and wet scrubbing) capable of reducing NOx emissions from stationary combustion sources by about 90%. However, methanol forms CO in flue gas as a byproduct Hydrogen peroxide and H2O2/CH3OH mixtures decrease the amount of CO formed from CH3OH and can substitute methanol in the CombiNO(x) process. This paper presents experimental and modeling results on H2O2 and H2O2/CH3OH reactions with NO in a 300 kW combustor firing natural gas and coal. Maximum NO oxidation was achieved at 750-820 K for injection of H2O2 and 1:1 H2O2/CH3OH mixture, and at 850-930 K for CH3OH injection. NO-to-NO2 conversion of 90-98% and 64-76% was achieved at an additive NO molar ratio of 1.5 during natural gas and coal firing, respectively. Influence of initial NO concentrations, the additive/NO ratio, oxygen and SO2 concentrations, and the presence of fly ash on process performance is discussed. Experimental results are qualitatively explained by kinetic modeling.