Studies of propene conversion over H-ZSM-5 demonstrate the importance of propene as an intermediate in methanol-to-hydrocarbons chemistry†
To investigate its role as an intermediate in methanol-to-hydrocarbons (MTH) chemistry, the reaction of propene over H-ZSM-5 zeolite at temperatures of 473, 573 and 673 K is studied over a period of 6 hours and the post-reaction catalysts examined by inelastic neutron scattering and ancillary analytical techniques. Low temperatures favour production of gasoline-range alkanes and alkenes, whilst the product distribution shifts to a primarily aromatic product stream as reaction temperature increases, with cyclopentadienyl intermediates from the aromatic formation process being detected spectroscopically in the reacted catalysts. The 473 K reaction deactivates the zeolite due to pore blockage from the growth of large, branched oligomer chains but coke build-up at higher temperatures is minimal and primarily consists of pure carbon. No evidence of immobilised poly-methylated aromatic species is observed at any temperature. A scheme for the full propene reaction series is proposed that involves a dual-cycle hydrocarbon pool mechanism like that found in MTH chemistry and supporting propene's role as an intermediate in that process. Minor differences in the product distribution of the propene-only reactions compared to classical MTH chemistry are identified due to the lack of a significant methylation reaction pathway that results in a more restricted range of substituted products.