SELECTIVE OXIDATION OF AMMONIA TO NITROGEN OVER SIO2-SUPPORTED MOO3 CATALYSTS

The (dis)similarities between the Selective Catalytic Reduction (SCR) of NO and the Selective Catalytic Oxidation (SCO) of NH3 are briefly reviewed. Since the SCO reaction acts counterproductively in the SCR reaction the two processes are related. A series Of V2O5, MoO3, and WO3 catalysts on various supports have been tested in the SCO reaction. It appears that an acid metal oxide in combination with an acid support gives the most active catalysts. The main byproduct is NO; minor amounts of N2O are formed. NO formation occurs in the temperature regime where the reduction of oxide lattice is faster than the recombination of two nitrogen atoms. High partial pressures of NH3 give rise to elevated selectivity to N2. This can be understood by assuming that the recombination probability of two nitrogen atoms becomes higher. A reaction mechanism, entitled the internal SCR mechanism is proposed to explain the formation of N2O.