Bert Weckhuysen#

Laudatio by Helmut Knozinger#


Weckhuysen has made landmark studies in the field of heterogeneous catalysis by using advanced spectroscopy to unravel active sites and related reaction/deactivation mechanisms. His remarkable innovative power can be characterized by: (a) the development and use of combined in-situ characterization methods and (b) the integration of optical microscopic and spectroscopic methods. These developments have allowed probing catalytic solids in a space and time resolved manner under true reaction conditions. This effort spans the whole range starting from the level of a lab-scale reactor (centimeters), extrudates (millimeters) and individual catalyst grains (micrometers) down to the level of a single metal nanoparticle (nanometers). An effort which can be best appreciated when considering his recent review article on these efforts (Weckhuysen, Angew. Chem. Int. Ed 2009, 48, 4910). Key to the success of the Weckhuysen group has been always the design of new set—ups to monitor catalytic processes under realistic reaction conditions.

A crucial aspect has been the direct linkibetween catalyst characterization and on-line activity and selectivity measurements. An example of such new experimental tool is the combination of time resolved in-situ XAFS, Raman and UV-Vis spectroscopy (Beale et al., Chem. Comm. 2005, 3015) to monitor in a synchronous manner spectroscopic and catalytic data. Based on this combined approach Weckhuysen has developed an on-line in-situ spectroscopic approach to control catalytic solids at work (Bennici et al., Angew. Chem. Int. Ed 2007, 46, 5412). Studies are currently under way to implement this successful concept in pilot-scale reactors.

In recent years Weckhuysen and co-workers have been successful in showing how in-situ spectroscopy can be used to map the catalytic properties of individual zeolite crystals (Kox et al., Angew. Chem. Int. Ed 2007, 46, 3652; Stavitski et al., Chem. Eur. J 2007, 13, 7057) revealing spatial heterogeneities in the architecture of these molecular sieves (Karwacki et al., Nature Materials 2009, 8, 959). This methodology has been complemented with the development of synchrotron-based in-situ IR microscopy (Stavitski et al., Angew. Chem. Int. Ed 2008, 47, 3543) and Coherent Anti-Stokes Raman Spectroscopy (CARS) (Kox et al., Angew. Chem. Int. Ed 2009, 48, 8990), providing an elegant way to study the reactivity of zeolites in 3-D. Instrumental in all these studies has been the use of a powerful probe reaction, i.e., the oligomerization of (substituted) styrene, to visualize Bronsted acidity within the nanoporcus channels of molecular sieves. Moreover, it has been shown that Bronsted acidity strength as well as aluminium distribution can be visualized in e.g. zeolites possessing mesoporosity (Kox et al., Chem. Eur. J 2008, 14, 1718). His most recent success in this field is the use of in-situ Scanning Transmission X-ray Microscopy (STXM) to monitor catalytic solids down to 10-30 nm (De Smit et al., Nature 2008, 456, 222; De Smit et al., Angew. Chem. Int. Ed 2009, 48, 3632). By using a specially designed reactor it was possible to monitor Fe-based Fischer-Tropsch catalysts not only during calcination and reduction, but also during CO hydrogenation at elevated temperatures. By doing so it was possible to identify regions of catalytic activity in which carbidic Fe phases could be observed.

Besides using in-situ spectroscopy to understand catalytic processes in great detail, the Weckhuysen group has also been able to translate fundamental concepts harvested with in-situ spectroscopic methods to design new catalyst materials. Elegant examples of such effort are the development of lanthanide-based catalysts for the destruction of chlorinated waste (Van der Avert et al,, Angew. Chem. Int. Ed 2002, 41, 4730) and synthesis of chemicals from such waste (Van der Heijden et al., Angew. Chem. Int. Ed 2008, 47, 5002). Furthermore Weckhuysen has made seminal contributions in the field of zeolite synthesis as well as in the fundamental of catalyst preparation. In the first topic, he has been able to elegantly show how porous oxides are constructed during a hydrothermal synthesis process starting from an amorphous synthesis gel by V using a combination of in-situ spectroscopy and scattering techniques. This work has been published in a series of JACS papers (Grandjean et al., J Am. Chem. Soc. 2005, 127, 14454; O’Brien et al., J Am. Chem. Soc. 2006, 128, 11744; Beale et al., J Am. Chem. Soc. 2006, 128, 12386).

Related to the fundamentals of catalyst preparation, the Weckhuysen group has been instrumental in visualizing as well as controlling in a space and time resolved manner the distribution of metal ions during the processes of impregnation, drying and calcination within catalyst extrudates. Examples include the development and use of non-invasive and invasive in-situ approaches to monitor Co—Mo HDS and Co Fischer-Tropsch preparation processes; namely Magnetic Resonance Imaging (Espinosa Alonso et al., J Am. Chem. Soc. 2009, 131, 16932; Bergwerff at al., Angew, Chem. Int. Ed 2007, 46, 7224; Bergwerff et al., Chem. Eur. J 2008, 14, 2363; Lysova et al,, J Am, Chem. Soc. 2005, 127, 11916), X—ray tomography (Espinosa Alonso et al., J Am. Chem. Soc, 2009, 131, 6525; Beale et al., Angew. Chem. Int. Ed 2007, 46, 8832), Raman micro-spectroscopy (Bergwerff et al., J Am. Chem, Soc, 2004, 126, 14548) and UV-Vis micro-spectroscopy (van de Water et al., J Am. Chem. Soc. 2005, 127, 5024; Bergwerff et al., Chem, Eur. J 2005, 11, 4592).

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