Conversion of bioethanol to propylene over ZSM-5 zeolites

The ethanol conversion reaction was systematically investigated over ZSM-5 zeolite catalysts with various Si/Al₂ ratios using different contact times and reaction temperatures, which produced similar product distributions over all catalysts at different contact times indicating that the product distribution has no relationship with the Si/Al₂. The mechanism of ethanol conversion was independent of the Si/Al2 ratio and propylene was directly produced via ethylene. Mechanistic analysis of the initial stage of the reaction suggested that ethylene was transformed to a carbene, which was a transient intermediate in the direct production of propylene. ZSM-5 zeolite was modified with phosphorus to improve propylene selectivity. Phosphorus-modified ZSM-5 catalysts showed enhanced selectivity for propylene production and good catalytic stability.