Testing and Development of New Catalysts for Vapor Phase Ammonia Oxidation 2003-01-2502
Catalytic oxidation is an effective means of controlling the build up of ammonia and other trace gas contaminants within closed spaces. However, it sometimes leads to the formation of noxious gases that need to be removed in post-treatment systems. In addition, ammonia removal is an issue when regeneration of water from wastewater is considered since ammonia is a byproduct of urea decomposition. For example, the VPCAR (Vapor Phase Catalytic Ammonia Reduction) advanced water processor system includes an oxidation reactor for the destruction of ammonia and of other volatile organics that are not separated out in the evaporator due to their volatility.
The oxidation of ammonia may produce nitrogen, nitrogen oxides (NO and NO2), nitrous oxide (N2O) and water vapor. The Spacecraft Maximum Allowable Concentration (SMAC) for NO and NO2 are respectively 4.5 and 0.5 ppm whereas the Threshold Limit Value (TLV) for N2O is 25 ppm. Therefore, minimization of nitrogen oxide formation is an important goal in developing ammonia oxidation catalysts for space applications.
On earth, because the removal of ammonia from air is environmentally important and because nitrogen oxides and nitrous oxide are greenhouse gases, university groups and catalyst manufacturers alike are devoting a large amount of research to the development of high efficiency, high selectivity catalysts for ammonia oxidation.
To address both these issues, Hamilton Sundstrand Space Systems International (HSSSI) has initiated an internally funded effort to compare the performance of commercially-available catalysts with HSSSI-manufactured catalysts for the oxidation of ammonia. The catalysts were compared based on their activity and selectivity, primarily at conditions representative of VPCAR applications. Testing to date demonstrated that HSSSI-made catalysts have both a higher activity than commercially available catalysts and a higher selectivity towards nitrogen.