Typical industrial olefin polymerization processes to produce both commodity and specialty polyolefin grades are mainly based on spherical, heterogeneous catalyst particles. During α-polymerization, heat from the exothermic reaction and pressure induced by the growing polymer chains on the catalyst particle lead to fragmentation, revealing active sites for further polymerization. To study these phenomena precisely and in-depth, we utilized a Nd-doped LaOCl-supported metallocene model system. This model catalyst can accurately display fluctuations in temperature with luminescence thermometry. During mild gas phase prepolymerization conditions, we observed a temperature difference of +43 °C and link this to the exothermicity of the ethylene polymerization reaction. In addition, the fragmentation behavior of the model catalyst was accurately monitored. The shell feature of the catalyst ruptured layer-by-layer, while the inner core fragmented via a bisectional fragmentation mechanism. We demonstrated that it is possible to probe the individual temperatures of multiple catalyst support particles within the field-of-view of the probe. This was correlated to structural changes and kinetics in an α-olefin polymerization catalyst. This powerful toolbox could be applied to different heterogeneous catalytic systems to correlate the temperature profile with morphological evolution.