The investigation of urea decomposition on catalysis

The main part of the air pollution that result from vehicles is the NOx gas that is given with the diesel exhaust. One of the most effective method to reduce these gases to harmless N2 is selective catalytic reduction (SCR) method which took place on the surface of a catalyst with the help of a reducing agent.In this study, the compounds, which are formed by decomposition of the urea (the effective reducing agent in the reduction of NOx) at the surface of the %1 Cu/Al2O3, %2 Cu/Al2O3, %2 Pt/Al2O3, %1 Ag/Al2O3, %2 Ag/Al2O3 and %5 Ag/Al2O3 catalysts that were prepared by the sol-gel method, were tried to be determined. The spectrums were taken by dropping the urea solution on the catalyst tablets and by using the FTIR at temperature betweeen 100?400º C. After the experimental study, it was observed that for all catalysts; there were peaks of OH, NH, CH stretching vibration bands as urea?s decomposition and hydrolysis compounds. Additionally C=O stretching vibration band, CO2, melamine, ammonia, ammonium and isocyanate peaks were observed. It was also observed that there were peaks of NH and adsorbed urea?s NH2 stretching vibration as the decomposition compound for some catalysts. As a decomposition compound of urea, isocyanate seemed in all catalysts but it gave the strongest peak for %2 Cu/Al2O3 at 250ºC. On the spectrum for the %1 Cu/Al2O3 at 100ºC the maximum amount of the decomposition compound was observed.On the spectrums which were taken at the temperatures that the %1 Cu/Al2O3, %2 Pt/Al2O3 and %2 Ag/Al2O3 catalysts gave the maximum NOx conversion, isocyanate was observed. For all catalysts that are mentioned above, it is possible to say that at all temperatures ammonia was formed. For these catalysts, at the spectrums when the conversion of NOX is reduced, the strongest melamine peak seemed. The urea decomposition compounds which were important for NOx conversion to ammonia, isocyanate and melamin were seen on the catalsyts.