RESUMO
Mono- and bimetallic alloy Pt and Ru catalysts supported on γ-Al2O3 have been investigated for the reduction of pollutants (NO x , NH3, and CO) generated during the continuous combustion of an aqueous urea ammonium nitrate fuel. A Pt/Ru alloy with a Pt25/Ru75 atomic ratio has been found to have higher activity and selectivity than those of a 50/50 alloy and monometallic catalysts. Among monometallic catalysts, Ru was more selective toward N2 formation, whereas Pt showed a higher selectivity toward NH3 formation. For Ru, it was observed that the oxidizing atmosphere of NO x pollutants caused the formation of RuO2, whereas Ru in the Pt/Ru alloy was stable under these conditions. Temperature (250-500 °C) and pressure (1-8 MPa) studies over Ru and 25/75 Pt/Ru have concluded that the alloy catalyst at 400 °C and 5 MPa reduced the pollutants to a minimum level with high yields of N2 (99.7%) and CO2 (99.9%). It was also observed that the 25/75 Pt/Ru catalyst remained stable up to 100 h of thermal treatment at 400 °C. Minimal pollutants were obtained at a weight hourly space velocity = 11 822 h-1. Characterization studies of the spent catalyst showed that metal particles were sintered over a period of time (8 h) and the γ-Al2O3 support was transformed into θ- and α-phases under the hydrothermal reaction conditions.
