Speaker
Dr
Alfons Molenbroek
(Haldor Topsøe A/S)
Description
The importance of large-scale facilities such as neutron and synchrotron sources in industrial catalysis still increases. Developments of new neutron- and synchrotron-based techniques both contribute to and are driven by developments in catalysis. The need to study catalysts at high temperatures and pressures in a reactive gas or liquid atmosphere resulted in the design and construction of in situ and operando reactors to perform structural characterization of catalysts under relevant reaction conditions. Neutron- and synchrotron-based techniques are especially versatile for the study of catalysts under reaction conditions due to the high penetrating power of neutrons and X-rays, the tunability of the energies over a broad range and the possibility to collect data with a high temporal and spatial extent. Several relevant properties such as elemental composition, chemical state, bond distances, particle sizes and size distributions, phase composition and the structure of the pore system can be studied by synchrotron-based methods. Similar and complementary information can be obtained by neutron-based techniques.
The development of single techniques such as XAFS to analogues with a high time resolution (QEXAFS) was broadened over the years to the combined use of several techniques, as no single technique can give all information necessary to understand the catalyst structure. Combinations of several in situ synchrotron-based techniques, e.g. XAFS/(A)XRD and SAXS/WAXS as well as the combination of synchrotron techniques with laboratory-based techniques such as XAFS/Raman and XAFS/IR-spectroscopy, were developed.
Also, the range of length scales has broadened over the years and with the advent of 3rd generation synchrotron sources, with highly brilliant beamlines, new options for studying catalysts and related nano-materials with a high spatial and temporal resolution were enabled. X-ray microscopy and X-ray tomography can be used to study the pore system of a catalyst and crack formation in catalyst tablets on many different length scales. Pore characterization is of crucial importance for heterogeneous catalysts, because the reactants and products have to be able to enter and exit the catalytic active sites present within the pores.
In this contribution some examples are given of the industrial use of some neutron- and synchrotron-based techniques for the understanding and development of heterogeneous catalysts. The use of in situ XAFS, AXRD and complementary neutron diffraction and SAXS for the characterization of Cu-based methanol-synthesis catalysts will be shown. Furthermore, the use of micro-tomography in industrial catalysis for the investigation of the pore system of DeNOx catalysts for removal of NOx from exhaust gasses and the study of cracks in catalyst tablets will be illustrated. Finally, some challenges for the collaboration between large-scale facilities and industrial users will be highlighted.
Primary author
Dr
Alfons Molenbroek
(Haldor Topsøe A/S)
