DEVELOPMENT OF A NOVEL CATALYST FOR NO DECOMPOSITION

Akyurtlu, Ates ; Akyurtlu, Jale F

Hampton University

关键词: Nitrogen Oxides;    Hydrocarbons;    Combustion;    Water Vapor;    Air Pollution;   

DOI  :  10.2172/882007
RP-ID  :  none
RP-ID  :  FG26-03NT41911
RP-ID  :  882007

美国|英语

来源: UNT Digital Library

【 摘 要 】

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 runs were made with feed gas mixtures containing water vapor. Two reaction regimes, one below and the other above 750 K were observed. Presence of water vapor slightly enhanced the catalyst activity, but decreased the selectivity towards N{sub 2} at low temperatures. For the current reporting period it was decided to Finish the runs with water vapor in the feed, check the effect of higher gas flow rate, and run experiments with catalyst treated at 900 K and 1000 K to drive off the OH groups. Unfortunately, shortly into the current period we had to change the gas feed preparation section. Then two flow controllers failed and we had to switch to rotameters and manual flow control as a stop gap measure. This affected the quality of the results and required repeated runs. Currently the results are satisfactory and the experiments are continuing. To take advantage of the down time the surface areas of the 15% Pt and 10% Pt catalysts were measured. The results indicate that when the catalysts are treated at 900 K for to hours to remove most of the OH groups on the surface, the activity of the 15% Pt catalyst increased.