Akademik Veri Yönetim Sistemi
Tezin Türü: Yüksek Lisans
Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Bilimleri Enstitüsü, Fen Bilimleri Enstitüsü, Türkiye
Tezin Onay Tarihi: 2014
Öğrenci: AYLİN CİVAN
Danışman: IŞIK ÖNAL
Özet:In this study, catalytic performances of Three Way Catalysts (TWC) are investigated via Density Functional Theory (DFT) methods and catalytic activity tests in a dynamic test system simulating the exhaust conditions of automobiles. DFT techniques are implemented by Vienna Ab Initio Simulation Package (VASP) and effect of manganese doping in TWC compositions are evaluated with computations on manganese, palladium and rhodium substituted ceria-zirconia mixed oxide (CZO) surface models. Carbon monoxide oxidation mechanisms and energetics are investigated on the model surfaces. Oxygen Storage Capacity (OSC) of CZO is remarkably enhanced by the synergistic effect of Pd and Mn doping. Accordingly, relative energy profile of CO oxidation mechanism on Pd-Mn substituted surface is found to be energetically most favored. Such an efficient collaboration is not observed with Rh and Mn doped CZO. In the experimental studies, TWC catalysts with varying compositions of Pd, Mn and Rh are synthesized via impregnation and solution combustion methods. Powder catalysts are then mixed with gamma alumina and washcoated on laboratory scale cordierite monoliths. Catalytic activity tests of the monolithic catalysts are carried out in a dynamic activity test system. Online data are simultaneously collected by a Mass Spectrometer (MS) and a CO analyzer coupled to the test system. Performance of the catalysts are evaluated by means of light-off temperatures. Activity results of 28 tests are examined in terms of thermal aging and SO2 exposure. In compliance with the findings of the computational studies, catalytic performance is improved when Pd is coupled with Mn in catalyst compositions in both synthesis techniques.