2018 Volume 61 Issue 1 Pages 20-27
The ethanol conversion reaction was systematically investigated over ZSM-5 zeolite catalysts with various Si/Al2 ratios (73, 128, 176, 207) using different contact times and reaction temperatures. The reaction yielded similar product distributions over all catalysts at different contact times, indicating that the product distribution has no relationship with the Si/Al2 ratio. Catalytic activity was proportional to the number of Brønsted acid sites. 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.
