Li, Wenqian; Li, Wanting; Cao, Xinxin; Chen, Longfei; Qin, Yibo; Zhu, Yanfeng; Zhang, Yanfei; Miao, Gai; Kong, Lingzhao; Li, Jiong; Chen, Xinqing

SCIENCE CHINA-CHEMISTRY

2024, 67, 1869-1870

Li, Wenqian; Li, Wanting; Cao, Xinxin; Chen, Longfei; Qin, Yibo; Zhu, Yanfeng; Zhang, Yanfei; Miao, Gai; Kong, Lingzhao; Li, Jiong; Chen, Xinqing

The application of non-noble metal catalysts in the catalytic direct gas-phase epoxidation of propylene with H2 and O2 to produce propylene oxide is valuable and challenging. The introduction of alkali metal promoters is one of the effective methods to improve the catalytic activity of catalysts. Herein, a series of alkali metal (Li, Na, K, Rb, and Cs)-promoted Ni/TS-1 catalysts were prepared to deeply understand the effect of alkali metals on the structure-activity relationship for gas-phase epoxidation of propylene. Among them, the Na-Ni/TS-1 catalyst exhibits the highest catalytic activity (propylene conversion of 7.35% and PO formation rate of 157.9 g h-1 kgcat-1) and the best stability (long-term stability exceeding 140 h at 200 degrees C). X-ray absorption and photoelectron spectroscopy revealed that the electronic structure of Ni can be tuned by the addition of alkali metal promoters. NH3-TPD-MS, CO2-TPD-MS, and C3H6-TPD-MS results indicate that the acidity of the catalyst can also be adjusted by the introduction of alkali metal, whereas the Na-Ni/TS-1 catalyst exhibits the strongest C3H6 adsorption capacity. Thus, the suitable acid-base properties, unique electronic properties of Ni species, and the strongest propylene adsorption capacity resulted in improved propylene gas-phase epoxidation activity of Na-Ni/TS-1 catalyst. This study not only provides a new strategy for the practical application of nickel-based catalysts in the gas-phase epoxidation of propylene but also provides insights into the promoting effect of alkali metals.