Improved catalyst formulations for the conversion of glycerol to bio-based aromatics

Abstract

The catalytic conversion of glycerol to aromatics (GTA, e.g., benzene, toluene, and xylenes, BTX) over a shaped H-ZSM-5/Al₂O₃ (60/40 wt%) catalyst was investigated in a continuous fixed-bed reactor to study the addition of the Al₂O₃ binder in the catalyst formulation on catalyst performance. The experiments were performed under N₂ at 550 °C, a WHSV of glycerol (pure) of 1 h⁻¹, and atmospheric pressure. The spent H-ZSM-5/Al₂O₃ catalysts were reused after an oxidative regeneration at 680 °C and in total 5 reaction-regeneration cycles were performed. Catalyst characterization studies show that the addition of the Al₂O₃ binder does not affect the surface area and crystallinity of the formulation, but increases the total pore volume (mesopores in particular) and total acidity (Lewis acidity in particular). The H-ZSM-5/Al₂O₃ (60/40 wt%) catalyst shows a considerably prolonged catalyst life-time (8.5 vs. 6.5 h for H-ZSM-5), resulting in a significant increase in the total BTX productivity (710 vs. 556 mg g⁻¹ H-ZSM-5). Besides, the addition of the Al₂O₃ binder retards irreversible deactivation. For instance, after 3 regenerations, catalyst performance is comparable to the fresh one. However, after 4 regenerations, some irreversible catalyst deactivation occurs, associated with a reduction in total pore volume, crystallinity, and acidity (Brønsted acidity in particular), and meso-porosity of the Al₂O₃ binder. This study shows that both the stability and reusability of H-ZSM-5-based catalysts for GTA are remarkably enhanced when using a suitable binder.