Propane dehydrogenation catalyzed by gallosilicate MFI zeolites with perturbed acidity

Abstract

The propane dehydrogenation (PDH) behavior of gallosilicate MFI catalysts synthesized in the presence of 3-mercaptopropyl-trimethoxysilane (MPS) is investigated. MPS addition to the zeolite synthesis gel results in gallosilicate molecular sieves with reduced Brønsted acidity and enhanced Lewis acidity, as shown by combined NH3 temperature-programmed desorption (TPD), isopropylamine (IPA) TPD and IR analysis of pyridine-loaded catalysts. In particular, the gallosilicate MFI catalysts prepared using MPS provide a significant concentration of strong Lewis acid sites, which are important in controlling the selectivity of PDH. Enhanced PDH performance with higher propane conversion rates and improved propylene selectivity with limited cracking and aromatization products are obtained from the catalysts synthesized with MPS. The gallosilicate MFI materials prepared using MPS are compared with a benchmark chromia-alumina catalyst, and the gallosilicate materials have a lower rate of deactivation (>50% lower) but slightly inferior propylene selectivity (Ga-MFI: 75%; Chromia-Alumina: 85%).