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Addition of NO lowers the temperature the hydrocarbon oxidizes in the gas phase drastically hexane ~ 390 °C Not only that, through the reaction mechanism in the gas phase a lot of NO 2 and oxygenated hydrocarbons form; these byproducts will have some impact on the catalytic reactions for the treatment of this exhaust 0 20 40 60 80 100 100 250 400 550 700 850 Conversion Hexane [%]/ Concentration aldehydes [ppm] Inlet gas Temperature [°C] Hexane conversion Formaldehyde Acetaldehyde Hexane conversion Formaldehyde Acetaldehyde Low temperature combustion engines emit higher hydrocarbon concentrations, and very low NO X concentrations this condition is very favorable for homogeneous oxidation of hydrocarbons • Addition of diethyl ether to reaction mixture does not effect the light- off temperatures of CO or hydrocarbons greatly • However much lower temperature of NO oxidation reaction onset is achieved (~70 °C), and a much higher percent of NO is oxidized with the addition of diethyl ether (91% versus 58%) 1. J. Zádor, C. A. Taatjes, R. X. Fernandes, Progress in Energy and Combustion Sciece, 37 (2011) 371-421. 2. K. Otsuka, R. Takahashi, K. Amakawa, I. Yamanaka, Catalysis Today, 45 (1998) 23-28. 3. K. Otsuka, R. Takahashi, I. Yamanaka, Journal of Catalysis, 185 (1999) 182-191. 4. N. I. Butkovskaya, A. Kukui, N. Pouvesle, G. Le Bras, Journal of Physical Chemistry A 109 (2005) 6509-6520. Coupled Heterogeneous and Homogeneous Hydrocarbon Oxidation on Bimetallic Pt-Pd/Al 2 O 3 Catalysts for Low Temperature Combustion Exhaust Melanie J. Hazlett and William S. Epling Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX Background Experimental Methods Homogeneous Oxidation References Acknowledgement We would like to thank the National Science Foundation and the US Department of Energy for their financial support in this work. • All catalysts prepared with molar equivalent of 1 wt% Pt • 1:1 Pt:Pd bimetallic mononlith catalysts supported on Al 2 O 3 washcoated onto cordierite honeycomb by Johnson Matthey; precious metals impregnated via incipient wetness in house • Temperature programmed oxidation (TPO) experiments used to screen catalyst performance; outlet concentrations measured with FTIR; hydrocarbon screenings done with 250 ppm of hydrocarbon with 5% CO 2 , 5% H 2 O, without and with 25 ppm NO in balance N 2 in an empty quartz tube reactor • Effect on catalyst tested in various operating conditions; varying CO, NO, hydrocarbon concentrations Autoignition temperature various hydrocarbons, atmospheric pressure J.M. Kuchta, Summary of Ignition Properties of Jet Fuels and Other Aircraft Combustible Fluids, 1975. Heterogeneous Oxidation Objective and Approach Want to harness the power of homogeneous oxidation and the byproducts thereof to enhance catalyst performance First step was hydrocarbon screening • Find a hydrocarbon that oxidizes homogeneously at a low enough temperature to be interesting to study catalyst chemistry • Evaluate if we can get any boost in catalytic performance by adding a hydrocarbon that will oxidize in the gas phase • Any positive effect from the NO oxidation or hydrocarbon fragments produced in free radical gas phase reactions 5500 ppm CO, 180 ppm C 12 H 26 , 65 ppm C 2 H 6 , 75 ppm C 2 H 4 , 20 ppm NO, 14% O 2 , 5% H 2 O, 5% CO 2 , Balance N 2 0 10 20 30 40 50 60 70 80 90 100 100 150 200 250 300 350 400 Conversion Dodecane [%] Temperature [°C] Blank Tube 1:1 Pt:Pd Catalyst 0 25 50 75 100 150 200 250 300 350 400 Concentration [ppm] Temperature [°C] Blank Tube NO2 Blank Tube Acetaldehyde 1:1 Pt:Pd Catalyst NO2 1:1 Pt:Pd Catalyst Acetaldehyde Dark: 250 ppm hexane, 25 ppm NO, 10% O 2 , 5% CO 2 , 5% H 2 O, balance N 2 Light: 250 ppm hexane, 10% O 2 , 5% CO 2 , 5% H 2 O, balance N 2 Small amount of NO helps a lot! Hydrocarbon Screening 0 20 40 60 80 100 100 250 400 550 700 850 Conversion Hydrocarbon [%] Inlet gas Temperature [°C] 0 5 10 15 20 25 100 250 400 550 700 850 Concentration NO 2 [ppm] Inlet gas Temperature [°C] 250 ppm hydrocarbon, 25 ppm NO, 10% O 2 , 5% CO 2 , 5% H 2 O, balance N 2 Gas phase oxidation mechanism with NO Gas phase oxidation mechanism without NO + → + → ∙ + ∙ + → ∙ + → → ∙ + ∙ → , , + → ∙ + ∙ ∙ + → ∙ ∙ → + ∙ ∙→ ′ + ∙ ∙ → + ∙ Lower temperature, more oxygenated products ∙ + → + → ∙ + ∙ ∙ + → ∙ + • High hydrocarbon and low NO X concentrations present in the exhaust of low temperature combustion engines promote homogeneous oxidation of hydrocarbons • Hydrocarbons were screened for this property as well as the NO 2 formation from oxidation evaluated • NO oxidation to NO 2 is favorable for NO X reduction catalysts, and potentially hydrocarbon selective catalytic reduction reactions • The potential to inject hydrocarbons in the exhaust that have very low temperature oxidation to promote the NO oxidation in the gas phase is being explored • The effect of this on catalytic performance of the diesel oxidation catalyst is being investigates Conclusions and Present Work ∙ + → Chain termination high NO concentration 1:1 Pt:Pt/Al 2 O 3 catalyst; inlet gas concentration 5000 ppm CO, 70 ppm C 2 H 6 , 70 ppm C 2 H 4 , 250 ppm C 12 H 26 , 25 ppm NO, 10% O 2 , 5% CO 2 , 5% H 2 O, 250 ppm diethyl ether, balance N 2 0 5 10 15 20 25 0 20 40 60 80 100 120 160 200 240 280 320 360 400 NO X Concentration [ppm] Conversion [%] Inlet Gas Temperature [°C] CO Ethylene Ethane Dodecane DEE NOx NO NO2
