BENZENE AND THIOPHENE FORMATION FROM ACETYLENE ON SULFIDED PD(111) STUDIED BY LITD FTMS

We report the first laser-induced thermal desorption (LITD) studies of acetylene on Pd(111). LITD coupled with Fourier transform mass spectrometry (FTMS) probes the surface molecular composition. Our results show simultaneous formation of thiophene and benzene at 120 K after a 6 L dose of acetylene at 80 K on a Pd(111) surface with 0.06 ML of sulfur. Simultaneous formation implies that formation of the C4H4 intermediate is the slow step in the formation of both cyclic products. The relative amounts of thiophene and benzene observed with LITD/FTMS are comparable, while thermal desorption spectroscopy (TDS) yields integrated thiophene signals that are < 2% as intense as for benzene. This indicates that thiophene primarily decomposes upon heating. Low coverage (0.5 L) results confirm reports that the presence of sulfur enhances benzene production.