Effects of Zn on catalytic performances of PtSn/Al2O3 in propane dehydrogenation

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. © 2019, Chemical Industry Press. All right reserved.