Space and Time Resolved Spectroscopy during the Preparation of Hydrogenation Catalyst Bodies

Abstract

The development of space and time resolved spectroscopic methods to image space and time dependent heterogeneities in catalyst bodies during preparation is of paramount importance for the development of more efficient and sustainable chemical processes. There are a large number of physicochemical parameters that play an important role in the preparation of catalyst bodies, and in order to obtain the optimum and most efficient catalyst material a careful selection of all these must be made. The aim of this work was double. On the one hand, new spatiotemporal spectroscopic methods were developed and their limitations and capabilities to study the different elemental steps of catalyst preparation were investigated. On the other hand, research on the influence of different chemical or physical properties during the preparation of Ni and Pd/gamma-Al2O3 catalysts was conducted by means of the developed spectroscopic techniques. Several spectroscopic techniques have been investigated comprising invasive (UV-Vis and IR micro-spectroscopies) and noninvasive methods (MRI and TEDDI). UV-Vis micro-spectroscopy provides information regarding the surroundings of the metal-ions during the impregnation step. Hence, the dynamics of the metal-ion and potential changes in its coordination sphere while moving towards the core of the catalyst body can be measured. This technique can also be applied to dried samples and, if the sample does not become black, after calcination or thermal treatment. IR micro-spectroscopy can be utilized on dried samples and it yields information regarding the location of organic molecules. On the other hand, magnetic resonance imaging (MRI) and tomographic energy dispersive diffraction imaging (TEDDI) have been investigated as noninvasive methods. 1H-MRI can be used in a very straightforward manner to monitor the impregnation process of paramagnetic metal-ion complexes and, when the ligands surrounding the metal-ion are water molecules, the impregnation process can be monitored quantitatively. The possibility of quantifying impregnation processes is of great importance in catalyst design since understanding the molecular-transport kinetics is crucial to control the preparation of mm-sized catalysts. Finally, the TEDDI technique is, for the moment, the only technique that can be used in situ during the drying and thermal treatment steps of mm-sized catalyst bodies preparation. Thanks to this advantage, the genesis of Ni nanoparticles within gamma-Al2O3 pellets has been visualized for the first time together with the breakdown of the precursor phase and the formation of, until now, unknown intermediate phases. Thus, this method can provide relevant input regarding the shape and size of the active particles in a catalytic material. Moreover, possible gradients of the shape and size of the active component along the catalyst body can be disclosed, which would provide enormous benefits when understanding the performance of the catalyst.