Adsorption and surface reactions of thiophene on ZSM5 zeolites

The adsorption and surface chemistry of thiophene on Na-, K-, and H-ZSM5 were studied by means of IR spectroscopy, mass spectrometry, and gravimetry. On hydroxyl groups, thiophene is reversibly adsorbed at room temperature via hydrogen bonding. On acid hydroxyl groups (strong Brönsted acid sites) ring opening and oligomerization were observed for longer exposures, indicating that these processes are relatively slow. The main primary products resulting from ring opening were concluded to be unsaturated thiol-like species. These species may undergo cracking while the fragments may rearrange to give various aromatic sulfur (and to a smaller extent sulfur free) compounds. The results indicate easy formation and breaking of sulfur carbon bonds on acidic zeolite catalysts.