The HIPPIE beamline went into full scale user operation in February 2018; and 11 external user groups (4 General Users + 7 Expert Users) so far performed experiments at HIPPIE. We will give a status update of the beamline and the endstation, talk about latest beamline/endstation performance (XPS at 30 mbar, sub s time resolution, etc) and discuss two different scientific case stories.
For many transition metal surfaces, it is possible to reach the so-called mass transfer limit (MTL) for simple reactions such as H2 or CO oxidation. Once in the MTL H2O or CO2 production is fully determined by gas diffusion through a H2 or CO depletion layer that is formed above the catalyst surface. Recently, planar laser-induced fluorescence (PLIF) was used to simulate a typical ambient pressure x-ray photoelectron spectroscopy (APXPS) setup and measure the size of the CO depletion layer [1]. In the first case story we will demonstrate how ambient pressure photoelectron x-ray spectroscopy (APXPS) can be used to probe the spatial gas composition above a catalytic active surface directly in the mass transfer limit (MTL) for the CO oxidation reaction.
The goal of many APXPS studies of catalytic model systems has been to identify the majority phase present when the catalytic model system is highly active. In contrast, the transition region where the catalyst surface change from one phase to another as a response to changes in temperature and/or gas composition is essentially unexplored. In the second case story, we will discuss our initial work with transient gas supply at HIPPIE and demonstrate how it is possible to follow the switching event from inactive to active catalytic phases in real time with ms time resolution using APXPS and at the same time measure the activity of the catalyst surface. In the talk we plan both to discuss CO oxidation on clean metal surfaces like Pd(100) as well as catalytic reactions performed under the cover of 2D films.
[1] Zhou et al. Catalysts, 7, 29 (2017)
Balasubramanian Thiagarajan et al.
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