Figure shows the product distribution typical for PP hydrogenolysis over other Ru catalysts, with Ru/CeO2 as the example. It has abundant C2-3 besides CH4, and wide distribution among liquid products centered around C22, while both liquid products and solid residue have no color. In contrast, Figure shows that Ru/TiO2-A-SG generates abundant C4-5 with minimal C2-3, the liquid products have a much narrower distribution centered around C10, and both liquid products and solid residue are light yellow (Figures and Since the high isomerization level and the lack of C1-2 products are typical characteristics for alkane hydrocracking, we suspect that Ru/TiO2-A-SG converts PP mainly through hydrocracking, instead of hydrogenolysis. In hydrocracking, C-C bonds are cleaved on Brønsted acid sites (BAS), and the metal only needs to catalyze dehydrogenation/hydrogenation. Thus, to test the hypothesis, we impregnated Ni and Pt onto TiO2-A-SG (0.07 M/nm 2 ), both of which are inert for C-C bond cleavage, i.e., hydrogenolysis, under these conditions. Figure shows that both Ni and Pt convert PP on TiO2-A-SG more efficiently than Ru, yielding similar product distribution (Figures and): no CH4, much more C4-5 than C2-3, narrow liquid distribution around C10, and yellow-colored products (Figure ). In addition, the TiO2-A-SG support alone, without any metal, can convert ~5% PP (Figure ), also with similar product distribution (Figure ). These results confirm that M/TiO2-A-SG can convert PP through hydrocracking, in which C-C bond cleavage occur on TiO2-A-SG, while the metal facilitates (de)hydrogenation steps. The presence of the more selective hydrocracking pathway on Ru/TiO2-A-SG explains its unique performance in PP upcycling in Figure . Since the two pathways on M/TiO2-A-SG exhibit very different selectivity between C4-5 and C2-3, we use the ratio between C2-3 yields and C4 yield (referred to as "(C2 + C3) / C4", cyan in Figure , C5 hard to quantify due to the high vapor pressure) as a reaction pathway indicator, along with the CH4 selectivity.