Effect of Unburned Methyl Esters on the NO_x Conversion of Fe-Zeolite SCR Catalyst

Engine and flow reactor experiments were conducted to determine the impact of biodiesel relative to ultra-low-sulfur diesel (ULSD) on inhibition of the selective catalytic reduction (SCR) reaction over an Fe-zeolite catalyst. Fe-zeolite SCR catalysts have the ability to adsorb and store unburned hydrocarbons (HC) at temperatures below 300°C. These stored HCs inhibit or block NO _x -ammonia reaction sites at low temperatures. Although biodiesel is not a hydrocarbon, similar effects are anticipated for unburned biodiesel and its organic combustion products. Flow reactor experiments indicate that in the absence of exposure to HC or B100, NO _x conversion begins at between 100° and 200°C. When exposure to unburned fuel occurs at higher temperatures (250°-400°C), the catalyst is able to adsorb a greater mass of biodiesel than of ULSD. Experiments show that when the catalyst is masked with ULSD, NO _x conversion is inhibited until it is heated to 400°C. However, when masked with biodiesel, NO _x conversion is observed to begin at temperatures as low as 200°C. Engine test results also show low-temperature recovery from HC storage. Engine tests indicate that, overall, the SCR system has a faster recovery from HC masking with biodiesel. This is at least partially due to a reduction in exhaust HCs, and thus total HC exposure with biodiesel.

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See papers presented at SAE 2009 Powertrains Fuels and Lubricants Meeting, November 2009, San Antonio, TX, USA, Session: Aftertreatment Systems (Part 3 of 3)

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