Alumina- and zirconia-alumina-loaded tin-platinum. Surface features and performance for butane dehydrogenation

Zirconia-loaded alumina samples were prepared and used as supports for platinum and tin metallic phases. X-ray diffraction patterns of 9.0 and 13.0 wt % ZrO2-loaded alumina samples showed the characteristic lines of the tetragonal ZrO2 phase. For the base alumina and these two supports, the nitrogen adsorption-desorption isotherms displayed type IV isotherms and a type H1 hysteresis loop characteristic of mesoporous materials, with BET areas and pore volumes decreasing with increasing ZrO2 content. Platinum and tin were incorporated into these substrates and then characterized by temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), and their performance in regard to n-butane dehydrogenation. The TPR profiles of the bimetallic systems revealed that platinum is readily reduced whereas tin reduction depends on the support, the metal loading, the preparation method, and the pretreatment conditions. All these systems were found to be highly selective toward olefins, with a minor contribution of the isomerization and cracking reactions. The catalysts became deactivated by coke deposition, although this deactivation was less marked in the Pt-Sn deposited on the ZrO2-Al2O3 substrates.