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

Propylene epoxidation with H2 and O2 to propylene oxide (PO) is a very valuable reaction. Considering the precious gold catalysts commonly used in the current research, the design of highly active non-noble metal catalysts is a huge challenge. Herein, we report a non-noble Ni/TS-1 catalyst, supported Ni nanoparticles on a hierarchical titanium silicate-1 (TS-1) zeolite by the deposition precipitation method, which exhibits desirable catalytic performance in the gas-phase epoxidation of propylene due to the strong metal–support interaction between Ni NPs and TS-1. Significantly, the prepared 2%Ni/TS-1 exhibited high PO selectivity of 76.8%, PO formation rate of 151.9 gPO/(h·Kgcat), and long-term stability at 200 °C. Notably, the catalytic performance of Ni/TS-1 is higher than that of the gold-based catalyst in the same condition. Furthermore, the reaction 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 the presence of nickel species was found to catalyze the reaction between hydrogen and oxygen, which could induce the formation of active radicals (•O2–, and •OOH) to achieve the in situ synthesis of H2O2 and subsequently oxidize propylene to PO. In addition, density functional theory (DFT) calculations indicated that the passivation layer on the Ni surface facilitates the production of H2O2. This work provides a promising way for the highly efficient catalyst on the selective oxidation with non-noble metals.