This Small Business Innovation Research (SBIR) Phase I project will investigate a new family of low-cost non-precious metal ammonia selective oxidation catalysts for use in selective catalytic reduction (SCR) systems. The selective catalytic reduction of NO with ammonia/urea is widely applied to combustion exhaust treatment for abating NOx emissions in power plants and diesel engine vehicles. A common problem of using the SCR technology is ammonia slip. Under conditions of incomplete NO conversion or exhaust temperature upswings, NH3 will slip into the exhaust, resulting in a number of environmental problems. This selective catalytic oxidation (SCO) technology can convert the toxic ammonia to nitrogen and water without introducing other reactants into the gas mixture. In this project, powder catalysts will be synthesized and tested at NexTech under simulated diesel engine exhaust atmospheres and characterized by physical and chemical methods. The broader/commercial impacts of this research are to solve the NH3 slip problem existing in the diesel engine SCR system with low cost, and to help reduce NOX emissions by greater than 90% in power plants when stoichiometric or excess amount of ammonia is used in the SCR process. The generated information can also provide new insights into understanding activation process of small molecules, such as NH3, NO, NO2 and O2, on the non-precious metal catalyst surface with acid and redox sites, enabling development of better catalysts for further emission reduction in the future.
In this Phase I SBIR project, NexTech Materials Ltd. conducted preliminary research to establish a new family of ammonia selective oxidation catalysts with excellent catalytic performance and sulfur tolerance for solving the ammonia slip problem existing in urea SCR systems, which is applied to abating NOx emissions from diesel engine exhaust. A number of transition metal oxides and ion-exchanged zeolites were prepared and mixed as catalysts for selective catalytic oxidation (SCO) of ammonia at low temperatures. The testing results indicated that the catalysts were highly active at 200-400°C and gas hourly space velocities (GHSVs) of 100,000-200,000 ml/g/h. 100 percent NH3 conversion was achieved at ≥ 225°C, with more than 90 percent converted to nitrogen. Also the transition metal oxide catalysts showed comparable SCO activity but higher N2 selectivity (i.e., less NO and N2O formation) as compared to a conventional Pt-based catalyst. Further, the catalysts were found to be tolerant to SO2 and H2O, which are present in diesel exhaust and are known to cause degradation in many catalyst materials. The preliminary results of the Phase I effort have demonstrated that the low-cost transition metal oxides are good catalyst candidates for ammonia removal. The results provide a clear path for developing superior SCO catalysts in Phase II.
