| Diesel engines operate at higher compression ratios and with a leaner fuel mixture which imparts the advantages of higher efficiency, higher reliability, high power output, lower exhaust temperature and lower carbon monoxide and hydrocarbon emissions. More and more attention is paid to diesel engines today for trucks, buses, and personal automobiles. At the same time, the emission regulations related to diesel engines are becoming more and more stringent. The catalytic reactor has been considered as the most effective way to reduce nitric oxide, which is one of the main components in diesel engine emissions.; Different kinds of transition metal loaded catalysts had been studied for NO reduction. Catalytic surface phenomena were investigated by use of surface specific analytical techniques including EDX, SEM, XRD, BET, and XPS. Specifically, the interaction of NO with the surface of the catalysts was investigated.; Several preparation and characterization techniques were performed during an initial screening phase. Transition metal copper, iron, cobalt, and cerium were tried as active sites. The Fe/γ-Al2O3 system showed interesting adsorption and desorption phenomena. The conversion data from the Horiba NO/NOx detector showed that copper active sites exhibit good performance with both γ-Al2O3 and ZSM-5 support materials.; Further investigation of the Fe/γ-Al2O3 system showed that it can adsorb NO at low temperature. The NO is desorbed as the temperature is increased. This process can be repeated several times. During the desorption process the mass spectrum was analyzed and showed nitrogen peaks at 14 and 28, and the oxygen peaks at 16, 32, 48, and 64. XPS experiments showed that the Fe2+ ion is the most active catalytic site. The ratio of the Fe3+/Fe2+ changed during the reaction and was an indictor of catalyst activity. Deactivation happened quickly during the reduction process. The data from BET denied the possibility of catalyst sintering and the data from XPS showed that the oxidation of Fe ions may be the main reason for catalyst deactivation. Also, a small amount of nitrogen was trapped on the surface of the catalysts after several runs which may be another possible reason for the deactivation.; Different copper oxidation states were also investigated as active sites. NO conversions versus temperature for different oxidation states were extremely different. The MS spectrum suggested that the possible products were N 2, O2, and a small amount of N2O. Kinetic data for NO decomposition on Cu+ were obtained and showed that the decomposition reaction was first order with NO concentration for both the ZSM-5 and γ-Al2O3 supports. The activation energy and the frequency factor for the Arrhenius equation for both supported catalysts showed the influence of the support material on the properties of the catalyst. |
