Abstract
To improve the understanding of catalysts, and ultimately the ability to design better materials, it is crucial to study them during their catalytic active states. Using in situ or operando conditions allows insights into structure-property relationships, which might not be observable by ex situ characterization. Spatially resolved X-ray fluorescence, X-ray diffraction and X-ray absorption near-edge spectroscopy are powerful tools to determine structural and electronic properties, and the spatial resolutions now achievable at hard X-ray nanoprobe beamlines make them an ideal complement to high-resolution transmission electron microscopy studies in a multi-length-scale analysis approach. The development of a system to enable the use of a commercially available gas-cell chip assembly within an X-ray nanoprobe beamline is reported here. The novel in situ capability is demonstrated by an investigation of the redox behaviour of supported Pt nanoparticles on ceria under typical lean and rich diesel-exhaust conditions; however, the system has broader application to a wide range of solid-gas reactions. In addition the setup allows complimentary insitu transmission electron microscopy and X-ray nanoprobe studies under identical conditions, with the major advantage compared with other systems that the exact same cell can be used and easily transferred between instruments. This offers the exciting possibility of studying the same particles under identical conditions (gas flow, pressure, temperature) using multiple techniques.
Highlights
Revealing the structure–activity relationship in catalysis is crucial to understanding the role of the catalyst during chemical processes and an essential step towards the ‘design of catalysts’
In situ studies are key to understanding materials under practical conditions by process replication on a smaller scale
Parker et al A cell design for nanoprobe and microscopy studies of catalysts measurements are critical to realizing new science, and many of the science cases for new low-emittance facilities are focused on exploiting flux gains for more dynamic studies
Summary
Revealing the structure–activity relationship in catalysis is crucial to understanding the role of the catalyst during chemical processes and an essential step towards the ‘design of catalysts’. The temperature of the heating spiral is moni- experiments, the sample dimension in the z direction should tored and controlled using the temperature-dependent resis- be limited to the hundreds of nanometres range due to the tance of the micro-heater, and manufacturing variations are limited penetration depth of the electron beam This thickness dealt with via a supplied chip-specific calibration which is constraint can be relaxed for X-ray only experiments. Steady-state simulations were carried out for various gas mass-flow rates at different inlet and outlet pressures and heater set-point temperature, for operation inside as well as outside the transmission electron microscope. The simulations show that the temperature above the heater inside the beam well, between the upper and lower half cell beam membranes, is uniform for several micrometres [Fig. 4(b)] This is very important as it allows us to exclude any cooling effect of the gas on the catalyst surface. As the catalyst particles are usually deposited on the central area of the chip, located on the thinned window areas for TEM imaging, the slight drop of temperature on the ‘external parts’ of the heater should not have any detrimental effect
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