Adsorption and Desulfurization of Thiophene on Nickel(111)

The adsorption and desulfurization of thiophene on clean and sulfided Ni(111) surfaces were studied with LEED, AES, TPR, and RAIS. The RAIS data indicate that thiophene adsorbs with its ring parallel or nearly parallel to the surface below room temperature. On clean Ni(111), thiophene polymerizes slightly above room temperature, as evidenced by paraffinic and aromatic C-H stretches in the reflection infrared spectrum and TPR product yields. Decomposition of the polymer aggregates produces a wide variety of hydrocarbons including C₅ fragments at 470 K. On a more acidic sulfided Ni(111) surface (θ_s= 0.19), thiophene appears to undergo electrophilic attack at an a-carbon as evidenced by TPR products and by methane evolution from the reaction of 2,5-dimethylthiophene. An electrophilic attack by a surface metal atom at an a-carbon of thiophene is discussed in terms of molecular orbital theory.