Abstract
Two in situ `nanoreactors' for high-resolution imaging of catalysts have been designed and applied at the hard X-ray nanoprobe endstation at beamline P06 of the PETRA III synchrotron radiation source. The reactors house samples supported on commercial MEMS chips, and were applied for complementary hard X-ray ptychography (23 nm spatial resolution) and transmission electron microscopy, with additional X-ray fluorescence measurements. The reactors allow pressures of 100 kPa and temperatures of up to 1573 K, offering a wide range of conditions relevant for catalysis. Ptychographic tomography was demonstrated at limited tilting angles of at least ±35° within the reactors and ±65° on the naked sample holders. Two case studies were selected to demonstrate the functionality of the reactors: (i) annealing of hierarchical nanoporous gold up to 923 K under inert He environment and (ii) acquisition ofa ptychographic projection series at ±35° of a hierarchically structured macroporous zeolite sample under ambient conditions. The reactors are shown to be a flexible and modular platform for in situ studies in catalysis and materials science which may be adapted for a range of sample and experiment types, opening new characterization pathways in correlative multimodal in situ analysis of functional materials at work. The cells will presently be made available for all interested users of beamline P06 at PETRA III.
Highlights
In the study of heterogeneous catalysis, derivation of structure –activity relationships is critical to unravel the role of catalysts in chemical processes as well as to improve their performance and stability
We previously described the design and application of closed in situ cells based on micro-electro-mechanical systems (MEMS) chips for X-ray ptychography (XRP) of catalyst materials, and studied morphological changes of colloidal gold nanoparticles and nanoporous gold catalysts during thermal annealing under specific gas atmospheres with spatial resolutions down to 20 nm (Baier, Damsgaard et al, 2016; Baier, Wittstock et al, 2016)
We present a series of new and improved in situ cells based on MEMS chips for complementary X-ray nanoimaging and spectroscopy measurements of catalysts and other functional materials using synchrotron radiation
Summary
In the study of heterogeneous catalysis, derivation of structure –activity relationships is critical to unravel the role of catalysts in chemical processes as well as to improve their performance and stability. While XRP is often used ex situ for many applications (Thibault et al, 2008; Hoppe et al, 2013; Piazza et al, 2014; Zhu et al, 2015; Wise et al, 2016; Sala et al, 2018), in situ imaging modes, on catalyst materials where accurate control of temperature and gas conditions is essential, have not been widely explored outside of a few pioneering works (Høydalsvik et al, 2014; van Riessen et al, 2017), including those from our group (Baier, Damsgaard et al, 2016; Baier, Wittstock et al, 2016; Baier et al, 2017) These studies still leave room for improvement in terms of spatial resolution, detection of possible reaction products and the application of complementary imaging modes [e.g. TEM and X-ray fluorescence (XRF)], as discussed below. Since the experimental demands of tomography are significantly more complex than for 2D imaging, performing PXCT in situ under precisely controlled gas and temperature conditions undoubtedly constitutes an even greater challenge than for in situ ptychography
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