Spatial Coupling of Metal and Acid Sites via Amorphous Nb–O–Al Interfaces for Selective Polyolefin Hydrocracking

Abstract Hydrocracking of polyolefin waste into liquid fuels over bifunctional catalysts requires efficient synergy between metal sites for H2 activation and acid sites for C–C bond cleavage. However, on nonzeolitic, oxide-based supports, these two functionalities are typically distributed in a random manner, limiting their spatial proximity and, consequently, the overall catalytic efficiency. Herein, we report an interface-design strategy that enforces nanoscale spatial coupling between metal and acid sites within a single structural unit, specifically tailored for polyolefin hydrocracking. The catalyst comprises highly dispersed rhodium (Rh) species anchored on an amorphous NbOx-doped γ-Al2O3 support. The amorphous Nb–O–Al interfaces generate electron-deficient Nb centers that function as medium-strong Lewis acid sites, while simultaneously modulating the electronic and coordination environment of the adjacent Rh species responsible for H2 activation. The nanoscale proximity of these complementary sites facilitates the coupling of acid-mediated C–C bond transformation with the subsequent hydrogenation of reactive intermediates. When applied to the hydrocracking of low-density polyethylene under mild conditions (240 °C, 2 MPa H2), the optimized Rh/10Nb–Al catalyst achieves a liquid product space-time yield of 283 gliquid·gmetal–1·h–1 with a methane selectivity of only 0.77%. Quantitative analysis reveals a linear correlation between the density of these interfacial strong Lewis acid sites and the hydrocracking activity, thereby directly linking the catalytic performance to the interfacial structure. This study establishes interfacial engineering as a rational strategy to encode metal–acid intimacy into the catalyst architecture, thereby offering a general design principle for selective plastic-to-fuel conversion.