Product gas evolution above planar microstructured model catalysts—A combined scanning mass spectrometry, Monte Carlo, and Computational Fluid Dynamics study

Abstract

The transport and distribution of reaction products above catalytically active Pt microstructures was studied by spatially resolved scanning mass spectrometry (SMS) in combination with Monte Carlo simulation and fluid dynamics calculations, using the oxidation of CO as test reaction. The spatial gas distribution above the Pt fields was measured via a thin quartz capillary connected to a mass spectrometer. Measurements were performed in two different pressure regimes, being characteristic for ballistic mass transfer and diffusion involving multiple collisions for the motion of CO(2) product molecules between the sample and the capillary tip, and using differently sized and shaped Pt microstructures. The tip height dependent lateral resolution of the SMS measurements as well as contributions from shadowing effects, due to the mass transport limitations between capillary tip and sample surface at close separations, were evaluated and analyzed. The data allow to define measurement and reaction conditions where effects induced by the capillary tip can be neglected ("minimal invasive measurements") and provide a basis for the evaluation of catalyst activities on microstructured model systems, e.g., for catalyst screening or studies of transport effects.

Nanostructured, mesoporous Au/TiO2 model catalysts – structure, stability and catalytic properties

“…The catalytic measurements were performed in a scanning mass spectrometer (SMS) system with a dedicated reaction chamber for reactions at pressures up to several mbar, and a separate second chamber containing a differentially pumped mass spectrometer (for details see [28–29]). The Au/TiO 2 samples were mounted on a heatable sample stage in the reaction chamber.…”

“…Hence, the gas flow into the volume enclosed by the cap is high enough under these conditions that the outgoing flow through the capillary does not lead to a measurable pressure drop in the reaction volume under the Ti cap (cf. [29]). The slow flow of reactants into and out of the reaction volume also results in an accumulation of CO 2 product gas within the reaction volume, which in turn leads to an enhancement of the CO 2 signal such that this can be reproducibly detected.…”

Mass spectrometric methods for monitoring redox processes in electrochemical cells

“…The pin‐hole was covered with a Teflon film (50 µm thick) and was brought in close proximity (a few micrometer) of the electrode. An improved version of miniaturized interface was presented recently (Jambunathan & Hillier, ; Jambunathan, Jayaraman, & Hillier, ; Wonders et al, ; Roos et al, ; Rus et al, ). The porous membrane was incorporated into the end of a capillary (0.15–0.6 mm inner diameter), and a three‐dimensional positioning system was used to bring the capillary in close proximity (10–100 µm) of the electrode (Fig.…”

Investigation of the oxygen storage capacity behaviour of three way catalysts using spatio-temporal analysis

“…Nevertheless by employing such analysis techniques, crucial intra-catalyst information is often lost within the monolith, especially regarding reaction profiles, intermediate formation, catalyst deactivation, reaction pathways and temperature evolution. To overcome such limitations a number of spatially resolved analysis techniques employing physical measurement probes have been developed, including fixed bed applications using IR, MS or GC analysis [30][31][32][33][34][35], monolith catalyst testing using spatially resolved capillary-inlet mass spectroscopy (SpaciMS) [36][37][38] modified with IR [39,40], or applied to foams [41], and other spatially resolved techniques including catalytic plate reactors [42,43] stagnation flow reactors (SFR) [44], scanning mass spectrometry (SMS) on microstructures [45,46], and other SpaciMS like techniques [47][48][49]. Although the insertion of physical probes can be considered invasive in some configurations, it has been shown via 3D CFD modelling that the probes can be considered non-invasive under specific conditions and configurations i.e.…”