OPTIMIZATION OF CHAR FOR NOx REMOVAL

Abstract

Work performed for this study demonstrates that the temperature of treatment and the identity of the treatment gas both strongly impact the surface chemistry of activated carbon. Two commercial activated carbons were treated in either N 2 or H 2 at different temperatures up to 2600 o C. Several techniques-including microcalorimetry, point of zero charge measurements, thermal desorption-were used to provide insight into important aspects of the chemical surface properties. The results show that activated carbons treated at high temperatures (ca. 950 o C) in hydrogen will not react with oxygen and water at ambient temperatures; moreover, surfaces created in this fashion have stable properties in ambient conditions for many months. In contrast, the same carbons treated in an inert gas (e.g., N 2) will react strongly with oxygen and water at ambient temperatures. In the presence of platinum (or any other noble metal), stable basic carbons, which will not adsorb oxygen in ambient laboratory conditions, can be created via a relatively low-temperature process. Treatment at higher temperatures (>1500 o C) produced increasingly stable surfaces in either N 2 or H 2. A structural model is proposed. To wit: Treatment at high temperatures in any gas will lead to the desorption of oxygen surface functionalities in the form of CO and/or CO 2. Absent any atom rearrangement, the desorption of these species will leave highly unsaturated carbon atoms ("dangling carbons") on the surface, which can easily adsorb O 2 and H 2 O. In an inert gas these "dangling carbons" will remain, but hydrogen treatments will remove these species and leave the surface with less energetic sites, which can only adsorb O 2 at elevated temperatures. Specifically, hydrogen reacts with any