Experimental Study of the Aging Effect on the Oxidation Catalyst Performance as an Emission Control Device for 4-stroke Gasoline Carburetor Motorcycles

Taheri, Arman | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54331 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Hamzehlouyan, Tayebeh
  7. Abstract:
  8. There are more than one million motorcycles in the city of Tehran that are responsible for significant amounts of various air pollutants emissions such as carbon monoxide and hydrocarbons. Oxidation catalysis, as the exhaust aftertreatment system of motorcycles, can reduce the emission of CO and hydrocarbon pollutants. The efficiency of these catalysts under typical operating conditions of vehicle exhaust gas has been studied in the literature. However, due to the specific features of motorcycles exhaust gas in Tehran, such as ultra-rich combustion, low air to fuel ratio (lambdas as low as 0.6-0.7), different exhaust gas composition and significant amount of lubricating oil consumption, selection of a highly active, durable and cost-effective catalyst for motorcycles in Tehran is still a challenge. Activity of these catalysts decreases over time due to the long-time exposure to high temperature exhaust gas conditions. Therefore, in the present work, an activity of a commercial Pt-Pd/Al2O3/CeO2 catalyst with wiremesh structure toward CO and C3H6 (as a representative of hydrocarbons) oxidation is evaluated under relevant operating conditions of Tehran’s motorcycles fleet. To study the catalyst durability, a simulated aging procedure is run at 900° C in the presence of water in a laboratory scale reactor system. The catalyst performance toward CO and C3H6 oxidation is examined over the aged catalyst sample. Also, characterization of the fresh and aged catalyst is carried out to evaluate its structural changes due to the aging process. To investigate the effect of oxygen concentration on the oxidation catalyst activity, all experiments are performed at four concentrations of oxygen, ultra-rich, rich, stoichiometry and lean conditions (corresponding to lambda values of 0.6, 0.8, 1.0 and 1.2, respectively). Simultaneous CO and C3H6 oxidation tests indicated the mutual inhibition effect of CO and propylene. According to the temperature-programmed oxidation (TPO) for the fresh catalyst, by increasing oxygen concentration, the light-off curve is shifted toward lower temperatures. Similar behavior is observed in simultaneous CO and C3H6 oxidation, indicating the beneficial role of oxygen on the oxidation reactions progress. Under the ultra-rich condition (lambda = 0.6), final conversion efficiency over the fresh catalyst is 94.4 and 44.1 percent for CO and C3H6, respectively. Upon implementing the aging, the catalyst activity is significantly reduced such that the catalyst T50 for CO oxidation increases from 336.6 ℃ under the lean conditions to 386 ℃ under the ultra-rich condition. The final CO conversion is reduced from 94.43% over the fresh catalyst to 67.2 % over the aged one. Final conversion of propylene is reduced from 44.1 over the fresh catalyst toward to 43.3% over the aged catalyst. It was found that the extent of catalyst deactivation upon aging becomes more significant as the exhaust condition is switched from the lean toward the ultra-rich condition. Characterization results indicated the agglomeration of catalyst particles and increased particle size after aging, leading to partial deactivation of the catalyst. According to these results, using secondary air injection (by pulse-air valves) upstream of the catalyst can lead to the improved catalyst performance and less significant catalyst deactivation
  9. Keywords:
  10. Oxidation Catalysts ; Catalytic Activity ; Gas Refine ; Exhaust Gases ; Aging ; Motorcycle Pollution

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