Dealing with a local heating effect when measuring catalytic solids in a reactor with Raman spectroscopy

Abstract

In continuation of our previous work on the applicability of the G(R N ) correction factor for the quantification of Raman spectra of coke during propane dehydrogenation experiments (Phys. Chem. Chem. Phys., 2005, 7, 211), research has been carried out on the potential of this correction factor for the quantification of supported metal oxides during reduction experiments. For this purpose, supported chromium oxide catalysts have been studied by combined in situ Raman and UV-Vis spectroscopy during temperature programmed reduction experiments with hydrogen as reducing agent. The goal was to quantify on-line the amount of Cr 61 in a reactor based on the measured in situ Raman spectra. During these experiments, a significant temperature effect was observed, which has been investigated in more detail with a thermal imaging technique. The results revealed a temperature 'on the spot' that can exceed 100 1C. It implies that Raman spectroscopy can have a considerable effect on the local reaction conditions and explains observed inconsistencies between the in situ UV-Vis and Raman data. In order to minimize this heating effect, reduction of the laser power, mathematical matching of the spectroscopic data, a different cell design and a change in reaction conditions has been evaluated. It is demonstrated that increasing the reactor temperature is the most feasible method to solve the heating problem. Next, it allows the application of in situ Raman spectroscopy in a reliable quantitative way without the need of an internal standard.

Raman study of NiFe2O4 nanoparticles, bulk and films: effect of laser power

“…After the advent of micro‐Raman instruments, the effect of incident laser power on sample degradation has been a major concern. In most of the earlier reports, the effect of power density has been attributed to temperature rise 2–4. However, in our recent study it was shown that, apart from thermal factors, electronic and other excitations can also significantly affect the Raman spectra 5.…”

“…The solid lines represent simulate curves using Eqns(1)and(2). The vertical lines on symbols represent error bars.…”

Chemical Imaging of Spatial Heterogeneities in Catalytic Solids at Different Length and Time Scales

“…In the last decade many attempts have been made to combine multiple spectroscopic techniques into one setup to perform correlative spectroscopy on the same catalyst material under identical conditions without the need for sample transfer. [87] This approach has lead to the development of different combined in situ setups, such as XRD / XAFS, [88] ESR / UV/ Vis, [89] Raman / UV/Vis, [90] NMR / UV/Vis, [91] Raman / IR, [92] XAFS / IR, [93] IR / UV/Vis, [94] XAFS / Raman / UV/Vis, [95] ESR / UV/Vis / Raman, [96] and XAFS / SAXS / WAXS / UV/ Vis / Raman (XAFS = X-ray absorption fine structure, SAXS = small-angle X-ray scattering, WAXS = wide-angle X-ray scattering). [97] Besides gathering complementary structural, electronic, and kinetic information on a catalytic process, these methods also allow evaluation of the reliability of the measurements by cross-checking two or more sets of spectroscopic data.…”

Resolving kinetics and dynamics of a catalytic reaction inside a fixed bed reactor by combined kinetic and spectroscopic profiling

“…For ex situ analysis the spheres were analyzed under a Raman microscope (Olympus, BX51WI) equipped with a 10Â objective. The laser power under the microscope was restricted to about 1 mW, avoiding beam damage to the sample as found by Tinnemans et al21 For comparison, about 25 mW laser power was used at the exit of the fiber Raman sensor inside the profile reactor without damaging the sample because the laser light leaves the beveled fiber tip unfocused. The illuminated area is estimated to be 30 times larger than that below the microscope (A fiber E 1 mm 2 vs. A microscope E 0.03 mm 2 ).Fig.…”