Ammonia oxidation over CuO/TiO2 catalyst: Selectivity and mechanistic study

Publisher Summary In this chapter, a CuO/TiO2 catalyst vapor (10wt% CuO, specific surface area = 120 m2/g) has been studied in NH3 oxidation. Catalysts based on CuO-TiO2 offer interesting properties among different formulations. However, selectivity to nitrogen can be decreased by the parallel formation of N2O and NO. The behavior of metal oxide catalysts upon these reactions can be influenced by water vapor that is always present in the reacting mixture. NH3 oxidation tests were carried out in a continuous flow fixed bed reactor, operating at atmospheric pressure, and a temperature, ranging from 200 to 350°C, with NH3 concentration in the feed of 200, 350, or 700 ppm; a constant concentration of O2 of 2.7%, a water vapor level, when present, of 400, 700, or 1000 ppm and a contact time of 4.5x10-3 s. In the chapter, NH3 temperature programmed desorption (TPD) spectra obtained with and without water vapor treatment are discussed. The spectrum obtained without water vapor treatment shows a composite peak with maxima at 172 and 258°C. As the CuO content of this catalyst is sufficient for the complete coverage of TiO2 surface, the signal is likely to be because of surface copper oxide species. The spectrum indicates at least two forms of NH3 adsorbed at weak to medium strength on copper oxide species. MS analysis of the effluent showed that NH3 is desorbed intact from the weaker sites, while it is oxidized to some extent to N2 on the stronger ones.