Selective Catalytic Reduction of NOx over Copper-based Microporous Catalysts

Abstract

Increasing concerns in our society regarding the release of harmful gasses into the atmosphere have led to the development and implementation of various technologies that curb the amount of pollutants released from various sources. Heterogeneous catalysts have made a major contribution in the control of such pollutants. One such family of pollutants, Nitrogen Oxides (NOx), originates from the use of fossil fuels in different applications, e.g. industrial processes, power plants, transport, etc. Analogous to the use of Three Way Catalysts (TWC) in cars with gasoline engines, Selective Catalytic Reduction (SCR) is an efficient technology realized for the control of NOx from diesel engines. State-of-the-art SCR technologies use Cu-based zeolites as the active catalyst. The aim of this PhD thesis was to contribute towards the understanding of the origins of the SCR process over Cu-based molecular sieves in the presence of NH3 as a reducing agent with a focus towards the structural properties of the catalyst. A part of the work involved synthesis of Cu-exchanged zeolites using different preparation techniques. The catalysts were pre-characterized using conventional laboratory techniques, such as UV-Vis-NIR diffuse reflectance (DR) spectroscopy and X-ray diffraction (XRD) and further studied for their catalytic activity under plug flow conditions, whilst following the output gasses online using infrared spectroscopy (IR) and mass spectrometry (MS). In addition, thorough characterization studies were performed using synchrotron based X-ray absorption (XAFS) and X-ray diffraction studies (XRD). Key to the task of active site elucidation was the combination of a technique sensitive to short range order (XAFS) with a technique sensitive to the long range order of materials (XRD).