Aromatization of iso-butanol with CO2 as an enhancer over ZSM-5 catalysts

Isobutanol was converted to aromatic compounds, such as BTX and C9 aromatics, over Ga or Zn impregnated ZSM-5 catalysts. The mechanism for aromatization includes dehydration, oligomerization, dehydrogenation, cyclization, and cycloaromatization according to referenced literature. Among these processes, dehydrogenation appeared to be the biggest hurdle to overcome; CO2 was expected to be consumed by removing hydrogen, facilitating formation of aromatic species via a reverse water-gas shift reaction (RWGS) of CO2 and hydrogen. The aromatization reaction was performed over H-ZSM-5, Zn-ZSM-5, and Ga-ZSM-5 catalysts under a He and CO2 stream, and enhancements to the yields of aromatics were observed when CO2 was flowed over the catalysts. Additional CO formed when the olefin/paraffin ratio increased as CO2 consumed H2, and this was also confirmed in the RWGS reaction. The biggest CO2 effect occurred over Ga-ZSM-5, and CO2 appeared to interact favorably with the Ga species on ZSM-5 according to XPS and ex situ FT-IR analysis. Thus, it was observed that CO2 served as a hydrogen scavenger and played a large role in enhancing the yields of aromatics.