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

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)(2)CO3 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 similar to 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.

Automated summary

In this study, post-treated Al-TS-1 catalysts were prepared through hydrothermal post-treatments, which showed higher H2O2 conversion in the HPEG process compared to the parent Al-TS-1. The post-treatment also affected the location and amount of framework Al species in the catalyst, but had minor impact on the EG selectivity.