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Synthesis and Evaluation of a Three-Way Catalyst for CO, Hydrocarbon and Nitrogen Oxide Emission Control in CNG-Fueled Vehicles

Esperi, Melika | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56056 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Hamzehlouyan, Tayebeh
  7. Abstract:
  8. According to the reports of the Tehran Air Quality Control Company, mobile sources are responsible for the emission of 70-85% of air pollutant in this metropolis. Over the past decades, compressed natural gas (CNG) is known as a cleaner fuel and a suitable alternative to gasoline and diesel fuels in the transportation section in some countries. However, methane emissions from natural gas vehicles is a significant challenge because it is a potent greenhouse gas and plays important role in global warming. In addition, because of another pollutant emissions from these vehicles, exhaust gas treatment is a crucial issue. Using Three-Way catalysts (TWC) is the conventional method in order to convert carbon monoxide, nitrogen oxide, methane and other unburned hydrocarbons. Common formulation for these catalysts includes Palladium, Platinum and Rhodium. Literature reviews show that using metallic promoters such as barium, cerium, zirconium, zinc, copper, and cobalt can be used as a catalyst promoter for converting methane. The aim of this study is to investigate the effect of different promoters namely Barium, Magnesium, Nickle, Zinc, Manganese and Copper on three-way catalyst in natural gas vehicles and recognize an appropriate ratio of platinum to palladium to reduce the cost of catalyst. Firstly, monometallic catalysts containing 2wt% palladium with 5wt% of the promoter (i.e. Barium, Magnesium, Zinc, and Copper) were synthesized by wet impregnation. Then, the precious metals ratio (Palladium, Platinum, and Rhodium) in three-way catalytic convertors for natural gas vehicles was optimized. At the end, the effectiveness of 5wt% of promoters (Ba, Mg, Mn, Zn, Cu, and Ni) on the selected optimal sample was studied. The properties, characteristics, and performance of these samples have been investigated by XRF, ICP-OES, H2-TPR, BET, and catalytic activity tests under conditions of natural gas vehicles exhaust. Results show that adding these promoters to monometallic catalyst with 2wt% palladium does not affect on the CO and CH4 light-off temperatures and has a negative effect on NOx light-off temperature. Among the samples containing the three precious metals (i.e. Pd, Pt, Rh), Pd3Pt1Rh0.2 represented the best activity. However, from an economic point of view and in order to reduce the cost of the catalytic converters Pd2.33Pt1.5Rh0.2 sample was introduced as the optimal trimetallic sample. Results of adding 5 wt% promoters to the Pd2.33Pt1.5Rh0.2 sample indicate that Mg is the best promoter which is added to the trimetallic selected sample considering all reactions. Moreover, it was illustrated that the temperature of 50% conversion of methane and carbon monoxide in the two samples Pd2.33Pt1.5Rh0.2/Mg/CZA and Pd3Pt1Rh0.2/CZA are not significantly different, but the temperature of 50% conversion of NO in the sample containing magnesium is about 23 ℃ lower. Overall, Pd2.33Pt1.5Rh0.2/Mg/CZA is more functional and economical compared to Pd3Pt1Rh0.2/CZA
  9. Keywords:
  10. Precious Metals ; Promoter ; Three Metallic Catalyst ; Palladium ; Platinum ; Rhodium ; Natural Gas Vehicles Three-Way Catalyst ; Pollution Removal ; Natural Gas Engines

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