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Modification of Three-Way Catalyst (Twc)Formulation for Gasoline Vehicles with the Goal of Improving Its Thermal Stability

Razmara, Shadi | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55353 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Hamzehlouyan, Tayebeh
  7. Abstract:
  8. Vehicle exhaust gas catalysts play a significant role in air pollution control. In order to solve the problems of cold start and limited supply of precious metals, new studies have focused on the development of three-way catalysts for gasoline vehicles with small amounts of precious metals and increase thermal stability. Different metal ions, especially rare earth metals, due to different physical and chemical properties, show different reinforcing effects on the properties of ceria-zirconia-based materials. Previous studies have shown that the enhancing effect of these materials and the ceria-zirconia ratio on catalyst activity and stability, as well as studies on thermal stability at 1050 ° C, are very limited. Most previous research has simplified catalyst formulation and operating conditions, so the results may differ from those of commercial catalysts; In addition, contradictory results have been found on the effect of inclusion of promoter metals on the modification of textural stability and ceria-zirconia structure. This work aims to investigate the effects of rare earth metals on the structural, textural, and redox properties of different supports. First, we chose the commercial supports with the highest specific surface area from the available options, then the Pd, Pt, and Rh-loaded catalyst powders were prepared. The fresh catalysts were aged at 1050 ◦C for 8 h with air/10% H2O, according to the Euro 5 standard, to investigate the thermal stability. The properties, characteristics, and performance of these fresh and aged samples have been investigated by XRD, H2-TPR, BET, CO-TPD, FESEM, and catalytic activity tests. For alumina-containing samples, a direct relationship was observed between hydrogen consumption and the light-off temperatures of pollutants, with CZA> CZLA> La-Al as the sequence of operation. Among the yttrium -containing samples, the two supports CZY and CZLYN are debatable due to their remarkable performance and major changes after thermal aging. Despite an 83% drop in the specific surface area of the CZY sample, the occurrence of redistribution in the CZY sample is very probable and the good catalytic activity of this sample after aging with operating temperature values of CO=160◦C, HC=353◦C and NO=381◦C is interesting. After aging, the CZLYN sample is also highly influenced by the metal-support interactions. This sample has the best performance of all catalysts in the fresh state, but its performance after aging, despite maintaining a surface area of 30.9 m2 / g, suffers a 20% drop in hydrogen consumption and its light-off temperature reaches to CO=195◦C, HC=384◦C, and NO=414◦C.

  9. Keywords:
  10. Gas Refine ; Exhaust Gases ; Thermal Stability ; Rare Earth Element ; Three-Way Catalyst ; Precious Metals

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