DEVELOPMENT OF A NOVEL CATALYST FOR NO DECOMPOSITION

Abstract

Air pollution arising from the emission of nitrogen oxides as a result of combustion taking place in boilers, furnaces and engines, has increasingly been recognized as a problem. New methods to remove NO{sub x} emissions significantly and economically must be developed. The current technology for post-combustion removal of NO is the selective catalytic reduction (SCR) of NO by ammonia or possibly by a hydrocarbon such as methane. The catalytic decomposition of NO to give N{sub 2} will be preferable to the SCR process because it will eliminate the costs and operating problems associated with the use of an external reducing species. The most promising decomposition catalysts are transition metal (especially copper)-exchanged zeolites, perovskites, and noble metals supported on metal oxides such as alumina, silica, and ceria. The main shortcoming of the noble metal reducible oxide (NMRO) catalysts is that they are prone to deactivation by oxygen. It has been reported that catalysts containing tin oxide show oxygen adsorption behavior that may involve hydroxyl groups attached to the tin oxide. This is different than that observed with other noble metal-metal oxide combinations, which have the oxygen adsorbing on the noble metal and subsequently spilling over to the metal oxide. This observation leads one to believe that the Pt/SnO{sub 2} catalysts may have a potential as NO decomposition catalysts in the presence of oxygen. This prediction is also supported by some preliminary data obtained for NO decomposition on a Pt/SnO{sub 2} catalyst in the PI's laboratory. The main objective of the proposed research is the evaluation of the Pt/SnO{sub 2} catalysts for the decomposition of NO in simulated power plant stack gases with particular attention to the resistance to deactivation by O{sub 2}, CO{sub 2}, and elevated temperatures. Therefore, it is proposed to perform temperature programmed desorption (TPD) and temperature programmed reaction (TPRx) studies on Pt/SnO{sub 2} catalysts having different noble metal concentrations and pretreated under different conditions. It is also proposed to perform NO decomposition tests in a laboratory-size packed-bed reactor to obtain long-term deactivation data. In the previous reporting period the GC-MS system was calibrated and the TPD runs for the 15% Pt/SnO{sub 2} catalyst after treatment with NO and subsequent treatments with NO and O{sub 2} were done. For these runs the catalyst was pretreated with dry helium for 2 hours at 40 C. The Temperature Programmed Reaction (TPRx) of NO and NO+O{sub 2} mixtures on the catalysts containing 15% Pt and 10% Pt were also performed. In this reporting period some TPRx runs with the catalysts containing 15% and 10% Pt were repeated due to the uncertainty of the oxygen content of the feed.