HETEROCYCLIZATION REACTION SITES ON THE SULFIDED PD(111) SURFACE

The sulfided Pd(111) surface is capable of cyclizing acetylene to both benzene and thiophene. We find that these reactions are sensitive to the temperature at which the sulfided surface has been prepared, occurring with greatest yield on surfaces produced at high temperatures (> 1000 K). Study of CO adsorption on these surfaces using both high-resolution electron energy loss spectroscopy and desorption measurements reveals that heating the surface introduces defects at which CO can bind in bridging sites between exposed Pd atoms. This defect concentration, as determined by CO adsorption in bridging sites, is correlated with the amount of thiophene produced from acetylene. It appears that acetylene heterocyclization is a defect-catalyzed reaction and that on the sulfided Pd(111) surface we are able to control defect density.