X-ray nanotomography uncovers morphological heterogeneity in a polymerization catalyst at multiple reaction stages

Summary During olefin polymerization on supported catalysts, the controlled morphological evolution of the catalyst particle is vital for ensuring optimal product properties and high catalyst activity. We employed non-destructive hard X-ray holotomography to quantitatively assess the 3D morphology of multiple silica-supported hafnocene-based catalyst particles during the early stages of gas-phase ethylene polymerization. Image processing and pore network modeling revealed clear variations in the dimensions and interconnectivity of pristine particles' macropore networks. This, together with apparent differences in the fragmentation behavior of pre-polymerized particles, suggests that the reactivity and morphological evolution of individual particles are largely dictated by their unique support and pore space architectures. By minimizing the structural heterogeneity among pristine catalyst particles, more uniform particle morphologies may be obtained. Significant polymerization activity, observed in the particles' interiors, further implies that appropriate polymerization conditions and catalyst kinetics can guarantee sufficiently high particle accessibilities and thus more homogeneous support fragmentation.