关键词: 丙烷脱氢, 锌助剂, 催化剂, 选择性, 稳定性

Abstract:

The PtSn/xZn-Al₂O₃ catalysts were prepared from platinum-tin carbonyl complexes by impregnation of the precursors on Zn-modified Al₂O₃ support. The effects of Zn on the catalytic performance of PtSn/Al₂O₃ catalysts in propane dehydrogenation were investigated. The physical structures, the surface acidities and the carbon deposition behaviors of PtSn/xZn-Al₂O₃ were studied by several techniques, including N₂ adsorption-desorption, X-ray diffraction (XRD), infrared spectra of pyridine adsorption (Py-IR), ammonia temperature-programmed desorption (NH₃-TPD) and transmission electron microscopy (TEM). The results showed that the pore sizes in PtSn/xZn-Al₂O₃ were mainly distributed between 8nm and 10nm. When Zn was added to PtSn/Al₂O₃ catalyst, ZnO species were formed, which could promote the metal particles to be smaller and more evenly dispersed on the surface of the catalysts. The acid quantity was reduced after Zn was added, especially for the acid sites with medium and strong Lewis acidity. With the increase of Zn loading, the acid quantity decreased firstly and then increased. The propylene selectivity and the stability of PtSn/Al₂O₃ catalysts were obviously improved by adding Zn promotor. However, the dehydrogenation activity decreased rapidly when the excess Zn was added. The optimized loading of Zn should be in the range of 0.75%—1.0% (mass fraction). The carbon deposited on the surface of the catalyst was mainly composed of olefin and aromatic hydrocarbons. The presence of Zn promoter could effectively inhibit the formation of deposited coke and improve the stability of the catalysts.

Key words: propane dehydrogenation, Zn promoter, catalyst, selectivity, stability