DCL International Inc.

Regeneration of Palladium Catalyst for Methane Abatement

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The exhaust gas of lean burn gas engines contains significant amounts of unburnt methane gas. Since methane is a strong greenhouse gas, reducing methane emissions would greatly improve the environment and provide greenhouse gas emissions credits. Oxidation catalysts containing platinum are commonly used for the elimination of non-methane hydrocarbons (all hydrocarbons except methane). The problem with platinum based catalysts is that methane is the most stable of the hydrocarbons. Because of this, platinum based catalysts are not very effective with methane and only eliminate a small fraction of methane contained in the exhaust gases under normal lean burn operating conditions. Since these platinum based oxidation catalysts are not very efficient, another method is desired and this paper will discuss another type of catalyst that can provide high methane conversion.  It has been reported in the literature that oxidation catalysts containing Palladium are very efficient in converting methane (typically greater than 80%). However, these palladium based catalysts are extremely sensitive to sulphur poisoning and their activities toward CH4 destruction deteriorate very quickly in the presence of SO2 or SO3. Since lean burn gas engines always contain a small amount of SO2 from lubricating oil or the natural gas itself (˜1-5 ppm SO2), it is very difficult to use palladium catalysts for methane abatement. In the first section, this paper will explain the deactivation mechanisms for palladiumbased catalyst in the presence of SO2. In a second section, the paper will discuss methods for maintaining high CH4 activity with palladium catalysts over a long period of time and in the presence of SO2 by means of continuously regenerating the catalyst. The paper will describe various methods for regenerating palladium-based catalyst. There are basically two ways for regenerating palladium-based catalysts. The first method is thermal regeneration and the paper will discuss the boundary conditions with its advantages and disadvantages. The second method is similar to what is being currently done with NOx adsorber catalysts. In order to regenerate the catalyst, the exhaust must periodically be in a rich condition with little to no oxygen present. The paper will discuss in detail what are the preferred operating conditions for successfully regenerating catalysts with rich conditions. With proper regeneration, it is believed that palladium based catalysts are an effective method for greatly reducing methane emissions from lean burn engines.

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