The partial oxidation of propane and the mechanism of selective catalytic reduction (SCR) of NO by propane over Ga2O3/Al2O3 in excess of O-2 have been investigated using in situ Fourier transform infrared spectroscopy. An optimized Ga2O3/Al2O3 catalyst shows high activity and efficiency of the reducing agent propane (100% conversion of NO at 623 K, GHSV: 10 000 h(-1)). One molecule of propane converts more than 4 NO molecules to N-2. The reaction starts with the partial oxidation of C3H8 by O-2 and carboxylates (acetate, formate) are formed on the catalyst surface above 573 K. This oxidation represents the rate-determining step of the SCR reaction. These surface carboxylates represent a dominating intermediate and (easily) react with (adsorbed) NO forming nitrogen-containing organic species. The latter are proposed to react with NO to form N-2. Total oxidation of propane was enhanced at temperatures above 773 K leading to decreased reductant efficiency. Surface nitrite and nitrate species can also be observed, but they were found to be spectators only. This could be concluded from the electron balance (conversion of propane relative to NO) and from the relative rates of the single reaction steps. On the basis of these investigations and stoichiometric calculations, a conclusive reaction mechanism is proposed.