Vibrational study of the interaction of acetylene and benzene on clean andcarbide-modified W(211) surfaces

As a part of a continuing investigation of acetylene reactions on tungsten surfaces covered by ultrathin metal films, the chemistry of acetylene on cl ean and carbide-modified W(211) surfaces has been investigated using high-r esolution electron energy-loss spectroscopy (HREELS) and temperature-progra mmed desorption (TPD) measurements. Acetylene decomposes between 100 and 45 0 K on the clean W(211) surface, ultimately forming carbidic carbon and gas eous hydrogen. During this decomposition process, a mixture of different hy drocarbon fragments are formed, most likely vinylidene (CCH2) pr vinyl (HCC H2) and acetylide (CCH). On the carbide-modified W(211) surface, acetylene also decomposes to produce carbon and gaseous hydrogen. However, compared t o clean W(211), the CH bond activation is suppressed on the carbide-modifie d W surface, as evidenced by the broadening and significant, shifting ai th e H-2 TPD features toward higher temperatures as well as by the HREEL spect ra monitoring the thermal decomposition of acetylene on the carbide-modifie d W(211) surface.