Transition Metal ion-exchanged zeolites can function as single-atom catalysts for several technologically important catalytic reactions. One such recent catalytic application of zeolites is the selective NOx catalytic reduction process that is currently under development in order to prevent emission of nitrogen oxides from modern diesel engines. In this process, ammonia reacts with nitrogen oxides in the zeolite catalyst in an oxidizing atmosphere to produce nitrogen and water. The small-pore Cu-ion exchanged zeolite Cu-SSZ-13 has been found to be a very efficient catalyst for this reaction. The characterization of the catalyst under operating conditions, in the presence of a complex catalytic environment that contains water vapor, oxygen, ammonia, nitrogen oxides and nitrogen, in a wide temperature range, has proved to be a difficult experimental task.In such complex material and catalytic environments, Reactive Molecular Dynamics based on empirical potentials can be very useful. Reactive force-fields are being extensively developed and used in large-scale MD simulations within the framework of the ReaxFF code. The force-fields are typically parameterized by fitting against DFT data. In this application we have developed a force-field that is capable of describing Cu-exchanged zeolites and their interaction with the reactive gas mixture. Using this force field in large-scale MD simulations we can understand important attributes of both the materials and the catalytic process, such as probing the chemical state and physical location of the Cu ions within the zeolite under operating conditions, assessing the hydrothermal stability of the catalyst and the relevant catalyst deactivation processes, high-temperature effects, the effects of gas-diffusion limitations, discovering the reaction pathways and intermediates, as well as predicting the effect of the zeolite structure on the reaction.

Hydrothermal stability and catalytic properties of Cu-exchanged zeolites: A reactive molecular dynamics study

248th National Meeting (2014)

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