Multi-Step TPSR/QMS Technique to Study the Kinetics of NH3-SCR

The context of the study is connected with the renewable sources of energy from biomass gasification (e.g. forestry residue, farming residue, municipal waste), to obtain biogas (H2, CO, CO2, N2, HCs) in gas engines. Gas engines (turbines) producing electricity or hot water provide energy at a local level. A major challenge is to develop appropriate catalytic technology for the treatment of exhaust gases (from the engine), to meet the new European Waste Incineration Directive (WID) for this type of a process. The problem of the exhaust gases installation lies in their immense size, ammonia slip, thermal deactivation (hot spots) and catalyst based on nobel metals. The remedy can be the application of the so called structured reactors based on metallic short channel structures of enhanced mass and heat transport [1] that are able to considerably shorten the reactor length. The application of such structures is entirely dependent on the development of new, highly-active catalysts with an increased conversion adjusted to high transport properties and also the methods of catalyst layering on the metallic surface. In line with the requirements stated by the structured reactors and the NH3-SCR process seem the copper-exchanged zeolites, which are known for their remarkable activity both in in the nitrogen oxides reduction and also in direct NO decomposition [3,4].
This work focuses on the optimization of the Catlab system equipped with tubular reactor and QMS for kinetic studies of NOx selective reduction with ammonia in the presence of oxygen. The equipment enables the multistep TPSR reactions including reduction, oxidation and desorption which used in a sequence provide the information on the active centres for the process. In this study. A real challenge is a proper calibration of the QMS detector for this kind of purposes. For this study the Cu2+-Y zeolite was prepared by exchanging the steamed form of NH4+-Y zeolite (LZY-82, Linde of Si/Alfram = 4.5) by three-fold ion exchange from aqueous solution of Cu(NO3)2 at 85oC.The sheets of kanthal steal were used as the catalyst carriers. As a reference the ZSM-5 zeolite was also tested. The catalyst was deposited on the surface of the precalcined (1000oC) and washcoated (Al2O3 or TiO2) surface of the carriers by impregnation. Both forms of the zeolite catalyst: powder and deposited one were subjected to further analyses. According to the results the most abandoned reactive intermediates during the reaction is oxygen and ammonia and reaction proceed through Rideal-Eley mechanism on Cu+ centres on zeolite cavities

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