Abstract
The two‐dimensional (2D) temporal evolution of the NO‐concentration over a NOx‐storage catalyst is investigated in situ with planar laser‐induced fluorescence (PLIF) in an optically accessible parallel wall channel reactor. Signal accumulated phase‐correlated 2D‐recordings of repetitive adsorption/desorption cycles are obtained by synchronizing the switching of the NO gas flow (on/off) with the laser and detection system, thereby significantly increasing the signal‐to‐noise ratio. The gas compositions at the reactor outlet are additionally monitored by ex‐situ analytics. The impacts of varying feed concentration, temperature and flow velocities are investigated in an unsteady state. Transient kinetics and the mass transfer limitations can be interpreted in terms of the NO concentration gradient changes. The technique presented here is a very useful tool to investigate the interaction between surface kinetics and the surrounding gas flow, especially for transient catalytic processes.
Highlights
The two-dimensional (2D) temporal evolution of the NOconcentration over a NOx-storage catalyst is investigated in situ with planar laser-induced fluorescence (PLIF) in an optically accessible parallel wall channel reactor
Since the concentrations are usually rather low, the single-shot PLIF images have a limited signal-tonoise ratio and several consecutive laser shots are averaged, resulting in an effective time resolution of about one second or more. Such a long acquisition time may not be suitable for the investigation of rapidly changing catalytic processes with high reactivity or short residence time, since the species distribution can vary significantly from laser shot to laser shot
We demonstrate spatially and temporally resolved PLIF measurements with a good signal-to-noise ratio and short acquisition time to investigate the transient NOx storage process
Summary
Sui Wan,[a] Yiran Guo,[b] Thomas Häber,[b] Rainer Suntz,*[b] and Olaf Deutschmann*[a, b]. Since the concentrations are usually rather low, the single-shot PLIF images have a limited signal-tonoise ratio and several consecutive laser shots are averaged, resulting in an effective time resolution of about one second or more Such a long acquisition time may not be suitable for the investigation of rapidly changing catalytic processes with high reactivity or short residence time, since the species distribution can vary significantly from laser shot to laser shot. The second approach has no such limitations, but requires that the process is reproducible and that the images are captured at the same phase within each cycle Such phase-correlated recordings are obtained in this study by synchronizing the flow switching valves (NOx on/off) with the laser pulses and the gating of the ICCD camera (details are given in the supporting information). Since the adsorption rate coefficient and the diffusion coefficient are constant at a given temperature, from Eq 2, one obtains
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