Boosting the deep oxidation of propane over zeolite encapsulated Rh-Mn bimetallic nanoclusters: Elucidating the role of confinement and synergy effects

Abstract

Metal nanocluster catalysts with superior activity and stability are urgently needed in the deep oxidation of volatile organic compounds (VOCs). In this study, a novel silicalite-1 zeolite confined rhodium-manganese bimetallic nano-cluster (1.6 nm) catalyst (Rh-MnOx@S-1) was designed and prepared by a simple one-pot method using a dual confinement strategy (shell confinement and strong metal-metal oxide interaction) and applied in the deep oxidation of propane. The results revealed that the temperature at 90% conversion (T90) for propane over Rh-MnOx@S-1 was as low as 264 °C, which is evidently higher than the conventional supported (Rh-MnOx/S-1, T90 = 369 °C) and the MnOx-free (Rh@S-1, T90 = 285 °C) catalysts. Moreover, the turnover frequency (TOF) value of Rh-MnOx@S-1 at 220 °C was up to 16 × 10−3 s−1, which is approximately 5–6 times higher than those of comparable catalysts. Most importantly, Rh-MnOx@S-1 also exhibited excellent high temperature thermal stability, water resistance and recyclability, which can be attributed to the confinement effect of the zeolite shell and the synergistic electronic-structure interaction between the Rh and MnOx species. The in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) analysis indicates that the C3H8 deep oxidation mechanism over Rh-MnOx@S-1 catalyst follows the Mars-van Krevelen (MvK) mechanism, i.e., the adsorbed C3H8 species reacted with the activated oxygen species from Rh-MnOx interfaces. The dual confinement strategy developed in this study provides a new way to design high performance catalysts for the removal of VOCs under harsh reaction conditions.