Fig. 1. Summary of experimental approach utilized in this study. (a) Schematic representation of polymers and catalysts utilized as well as three types of transport limitations identified. (b) Catalyst activity was investigated using non-isothermal thermogravimetric analysis of catalyst : polymer mixtures. The effect of catalyst structure and polymer molecular weight were investigated by determining the required cracking temperature at different catalyst : polymer ratios. Lower cracking temperature corresponds to higher effective activity. (c) The effect of mass transport limitations on selectivity was studied using semi-batch reactor experiments with (on-line) gas chromatography. (d) Catalyst–polymer interactions on a macroscopic scale were investigated using in situ optical microscopy, allowing to identify differences in catalyst–polymer contact for polymers of different Mw. Additionally, polymer entering inside the particle interior turns the particle more transparent to light by reducing scattering, allowing to qualitatively asses catalyst accessibility using simple optical microscopy. Scale bars: 100 μm. (e) On a microscale, electron microscopy of catalyst–polymer composites which were cut-open using a focussed ion beam allows to directly determine the accessibility of the catalyst pores. Micrographs were segmented for clarity. Scale bars: 3 μm.
