The reactions of propylene, propadiene, and methylacetylene with Rh(111) crystal faces in ultrahigh vacuum (UHV) from 80 to 800 K have been studied by low-energy electron diffraction (LEED), high-resolution electron energy loss spectroscopy (HREELS), and thermal desorption spectroscopy (TDS). All three hydrocarbons adsorb intact at 80 K. At this temperature, methylacetylene forms a p(2×2) LEED pattern while propylene and propadiene adsorb as disordered monolayers. Above 200 K, propylene and propadiene also form p(2×2) LEED patterns which are stable up to 270 K. The propylene fragment in this temperature range is propylidyne (CCH2CH3). By room temperature all the C3 hydrocarbons have decomposed to ethylidyne (CCH3) and polymerized CxH fragments. Surface hydrogen is instrumental in the C-C bond breaking, and partial deuteriation studies were performed to determine which C-C bonds break first. The ethylidyne species are stable up to 400 K, above which they decompose to CxH fragments. The bonding and the thermal decomposition pathways for propylene on Rh(111) are compared to Pt(111) surface chemistry.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry