Catalytically active species in bifunctional Aluminum-Containing titanium Silicalite-1 zeolite for ethylene epoxidation

Abstract

Aluminum-containing titanium silicalite-1 zeolite (Al-TS-1) is an important bifunctional catalyst for green production of ethylene glycol (EG) via a hydrogen peroxide/ethylene process (HPEG). In this work, hydrothermal post-treatments are carried out to a parent Al-TS-1 in (NH4)2CO3 aqueous solutions under varied conditions to produce post-treated Al-TS-1 catalysts. In addition to the framework Ti(OSi)4 species found in both the parent and post-treated Al-TS-1 catalysts, the post-treated catalysts also contain Ti(OH)4(OSi)2 species. For HPEG process, the post-treated Al-TS-1 delivers a significantly higher H2O2 conversion than the parent Al-TS-1. This is attributed to the outstanding catalytic activity of Ti(OH)4(OSi)2 which is ∼ 16.8 times the activity of Ti(OSi)4. Furthermore, although the parent and post-treated Al-TS-1 contain both the framework and extra-framework Al species, the post-treatment is also found to alter the detailed location and amount of framework Al species in the catalyst. Such changes, however, have only minor effect on the EG selectivity.