Chemical properties of carbon-modified titanium: reaction pathways of cyclohexene and ethylene over Ti(0 0 0 1) and C/Ti(0 0 0 1)

The reaction pathways of cyclohexene and ethylene on clean and carbon-modified Ti(0 0 0 1) surfaces were studied using high-resolution electron energy loss spectroscopy (HREELS) and temperature-programmed desorption (TPD). As typically observed for early transition metals, the clean Ti(0 0 0 1) surface interacted strongly with ethylene and cyclohexene upon adsorption at 100 K, leading to the complete decomposition to atomic carbon and hydrogen at higher temperatures. On the other hand, the C/Ti(0 0 0 1) surfaces showed chemical activity similar to Pt-group metals. The formation of carbon overlayers on Ti(0 0 0 1) resulted in the selective dehydrogenation of cyclohexene to produce gas-phase benzene. The reactivity of the C/Ti(0 0 0 1) surfaces toward ethylene was also very similar to those typically observed on Pt-group metal surfaces. At 100 K, ethylene molecules adsorbed to the C/Ti(0 0 0 1) surface in the di-σ bonded configuration, which was converted to an intermediate consistent with ethylidyne (CCH3) species by 300 K. The results reported here corroborate well with previous studies on C/V(1 1 0), C/Mo(1 1 0), C/W(1 1 1) and C/W(1 1 0). This manuscript also represents one of the first surface science investigations of the surface reactivity of Ti(0 0 0 1) and C/Ti(0 0 0 1).