The light microscopic images in Figure show the different planes of Raman mapping. The view from the top plane (xy) is indicated by a red rectangle, and the view from the vertical (zy) and horizontal (zx) planes are blue and green, respectively. The inner surface of the used reactors looks jagged and rough and the PTFE tubing has some inorganic deposits on the surface, which can be catalyst material. The size, in the range of a few micrometer indicate that these deposits are most likely fragments of the originally fractionated catalyst material. The fibers and fragments thereof identified with optical microscopy are not detected with Raman microscopy. This can be due to negligible signal intensity compared to the main signal, glass fibers or fragments which have no Raman signal or due to optical effects. Interestingly, the embossed particles can be seen in the Raman spectra of both inlet zones. However, the depth of the embossed spheres is less prominent than expected from the light microscopic images, in the range of a few micrometers, in the vertical and horizontal planes of the Raman maps.