Figure 3.

Mismatch between thermo- and mechano-catalysis. (A) Hypothetical catalytic pathways (C1–C3) to explain how a catalyst causes an increase in the formation of small hydrocarbons during ball milling. Noncatalytic, purely mechanochemical pathways are indicated with black arrows. (B) TGA profiles of model PP with sulfated (SZ), and untreated (ZrO₂) grinding spheres. (C) Molar mass distributions before and after milling waste PP with sulfated (SZ-800), and untreated (ZrO₂) grinding spheres for 10 and 60 h. (D) Propene formation during ball milling of model PP with sulfated (SZ), and untreated (ZrO₂) grinding spheres. (E) Raman spectra of sulfated (SZ), and untreated (ZrO₂) grinding spheres. Signals corresponding to monoclinic (m) and tetragonal (t) ZrO₂ are indicated. The surface of SZ-650 spheres is heterogeneous, and obtained spectra vary from spot to spot (Figure S24).