Highly Efficient Epoxidation of Propylene with In Situ-Generated H2O2 over a Hierarchical TS-1 Zeolite-Supported Non-Noble Nickel Catalyst

Propylene epoxidation with H-2 and O-2 to propyleneoxide (PO) is a very valuable reaction. Considering the precious goldcatalysts commonly used in the current research, the design of highlyactive non-noble metal catalysts is a huge challenge. Herein, we reporta non-noble Ni/TS-1 catalyst, supported Ni nanoparticles on a hierarchicaltitanium silicate-1 (TS-1) zeolite by the deposition precipitationmethod, which exhibits desirable catalytic performance in the gas-phaseepoxidation of propylene due to the strong metal-support interactionbetween Ni NPs and TS-1. Significantly, the prepared 2%Ni/TS-1 exhibitedhigh PO selectivity of 76.8%, PO formation rate of 151.9 g(PO)/(h & BULL;Kg(cat)), and long-term stability at 200 & DEG;C.Notably, the catalytic performance of Ni/TS-1 is higher than thatof the gold-based catalyst in the same condition. Furthermore, thereaction mechanism was investigated by various characterizations,including high-resolution transmission electron microscopy (HR-TEM),extended X-ray absorption fine structure (EXAFS), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS),and in situ electron paramagnetic resonance (EPR),proving that metallic Ni was the dominant nickel species, and thepresence of nickel species was found to catalyze the reaction betweenhydrogen and oxygen, which could induce the formation of active radicals(O-& BULL;(2) (-), and (OOH)-O-& BULL;) to achieve the in situ synthesis of H2O2 and subsequently oxidize propylene to PO. In addition,density functional theory (DFT) calculations indicated that the passivationlayer on the Ni surface facilitates the production of H2O2. This work provides a promising way for the highlyefficient catalyst on the selective oxidation with non-noble metals.