HETEROCYCLIZATION SITES ON THE SULFIDED PD(111) SURFACE

We have examined the heterocyclization of acetylene (C2H2) to thiophene (C4H4S) on the sulfided Pd(111) surface. This reaction has been found to occur at defects in the sulfided surface which can be produced either by annealing the surface to temperatures > 800 K or by sulfiding the surface to near-saturation. At 300 K both thiophene and CO will adsorb selectively at these defects and can be used to titrate the surface defect concentration. The yield of thiophene from the acetylene heterocyclization reaction is correlated with the defect concentration as measured by these methods and, hence, it appears that the reaction occurs at defects in the sulfided surface. Vibrational spectra indicate that CO adsorbed at these defects is bound in a bridging configuration between Pd atoms indicating that the defects expose the metallic substrate.