Development of a test protocol for evaluation of methane oxidation catalysts
Gianni Caravaggio, Natural Resources Canada, CanmetENERGY
Caravaggio*, L. Nossova, N. Maffei, R. Burich, P. Sutherland
Natural Resources Canada, CanmetENERGY-Ottawa, 1 Haanel Drive, Ottawa, Ontario K1A 1M1 Canada
*corresponding author: gianni.caravaggio@canada.ca
In recent years, the use of natural gas (NG) as a fuel in the transportation sector has received increased interest. NG vehicles (NGVs) are a cleaner alternative to gasoline and diesel vehicles and can provide a 15-25% reduction in total GHG emissions. More specifically, NG fuelled lean burn engines have performance characteristics similar to diesel engines. However, unburnt methane (CH4) exhaust emissions (CH4 slip) from these engines is a concern since CH4 is a more potent GHG than CO2 (up to 25x more). One strategy to eliminate methane slip is to implement exhaust after-treatment systems capable of catalytically oxidizing CH4 to CO2. Palladium based catalysts are the most active for the oxidation of CH4 but they deactivate from sulfur poisoning, with amounts as low as 1 ppm S, and in presence of water. Since lean burn engine exhaust contains sulfur compounds and large amounts of water vapor, it is essential to develop methane oxidation catalysts that are sulfur and water-resistant.
In this work, a testing protocol with performance metrics was developed for assessing CH4 oxidation activity of catalysts under simulated heavy-duty lean burn exhaust. It was determined that a minimum of 40 h of aging was needed to obtain a stabilized catalyst activity. T50 values obtained after 40 h on stream, with the addition of sulfur in the simulated NG feed, were used to assess and compare catalyst activities. Catalysts with T50 values below 500°C (upper temperature limit of NG exhaust) were chosen for further aging, up to a total of 500 h. It is proposed that catalysts with T50 values below 500°C after 500 h of aging would be acceptable candidates for testing on a NG engine. Using this test protocol, a series of catalysts on a commercial support were evaluated and a particular catalyst that showed high water tolerance and sulfur resistance after 500 h of aging was chosen for an engine test.
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