Beyond Morphology: Revealing Support-Active Phase Coupling in Spherical SiO2 and TiO2 Nanoreactors for Cu- and Co-Oxide-Catalyzed Toluene Combustion

Abstract

Disentangling the intrinsic contribution of support-active phase interactions remains a major challenge in heterogeneous catalysis, as conventional supported catalysts often combine variations in morphology, particle size, dispersion, and support chemistry. Herein, we introduce hollow SiO2 and TiO2 nanoreactors containing encapsulated transition metal oxide particles as model platforms for systematically investigating how chemically distinct oxide environments influence transition metal oxide catalysts during volatile organic compounds (VOCs) oxidation. Mesoporous amorphous SiO2 and anatase TiO2 shells with comparable diameters (500–600 nm) and similar textural properties were synthesized using polymeric spherical templates. Subsequent impregnation with 5–15 wt % Cu or Co, followed by calcination, yielded nanoreactors containing predominantly crystalline CuO or Co3O4 particles within the internal cavities. The CuO- or Co3O4-based systems exhibited fundamentally different support-active phase coupling. Strong interactions between CuO and TiO2 modified the Cu coordination environment without significant incorporation of Cu2+ into the TiO2 lattice, while ex situ XPS/XAS measurements indicated Cu+ as the dominant surface Cu species after air exposure. In contrast, Co3O4 interacted only weakly with the surrounding oxides, and its catalytic behavior was influenced primarily by crystallite size and oxygen reducibility. Consequently, the @TiO2_CuO and @SiO2_Co3O4 nanoreactors displayed the highest activity in toluene combustion. In situ DRIFT measurements revealed that TiO2 promotes the stabilization and conversion of oxygenated surface intermediates, whereas such species were largely absent within the SiO2 nanoreactors. Combined with H2-TPR results, these findings demonstrate that VOCs oxidation proceeds via the Mars-van Krevelen mechanism, with catalytic activity closely correlated with lattice oxygen mobility. This work establishes hollow oxide nanoreactors as powerful model systems for investigating support-active phase interactions beyond morphological effects and provides new design principles for VOCs abatement catalysts.