One-step synthesis of glycidol from glycerol in a gas-phase packed-bed continuous flow reactor over HZSM-5 zeolite catalysts modified by CsNO3

Abstract

In this work we report the pioneering gas-phase conversion of glycerol into glycidol in one-step over Cs–ZSM-5 zeolite catalyst with SiO2/Al2O3 = 1500. The structure and catalytic performance of catalysts synthesized by wet impregnation method with different Cs loadings were studied. The catalysts were characterized by ICP–MS, XRD, N2 physisorption, STEM–EDX, SEM, pyridine-DRIFT, CO2–TPD, NH3–TPD, and TGA techniques. The reaction was carried out in a packed-bed continuous flow reactor under atmospheric pressure. The highest achieved glycidol yield was 40.4 mol% over 20 wt% Cs–ZSM-5(1500) catalyst with 10 wt% glycerol in the feed at 350 °C reaction temperature and GHSVtotal = 1250 h−1. The glycidol selectivity was increasing steadily from 41.4 to 64.3 mol% during 27 h time-on-stream. This catalyst showed relatively high stability and selectivity, which was attributed to the presence of a suitable amount of basic sites and the strong CsNO3/HZSM-5 support synergetic interaction. Based on the identified reaction products, we propose the reaction mechanism of the catalytic glycerol conversion to glycidol over the tested catalysts. It was revealed by SEM and XRD that Si species partly dissolved from HZSM-5 framework after impregnation with CsNO3. Furthermore, we showed that the catalyst deactivation depends on the amount of CsNO3 active phase (basic sites) and the coke formation. The catalytic results demonstrate that at the beginning the glycerol conversion dropped down when CsNO3 was partly decomposed during the reaction, while the second deactivation stage with a slow decrease of catalyst performance corresponded to the coke formation.