| AVS 66th International Symposium & Exhibition | |
| Fundamental Discoveries in Heterogeneous Catalysis Focus Topic | Thursday Sessions |
| Session HC-ThP |
| Session: | Fundamental Discoveries in Heterogeneous Catalysis Poster Session |
| Presenter: | Ravi Ranjan, University of Illinois at Chicago |
| Authors: | R. Ranjan, University of Illinois at Chicago M. Trenary, University of Illinois at Chicago |
| Correspondent: | Click to Email |
The surface species formed following the adsorption and hydrogenation of acetylene (C2H2) on Pd(111) in the temperature range of 90-450 K are identified and characterized. The techniques used to detect the species are reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD). Acetylene was adsorbed at low temperature and then heated to 300 K where it converts to ethylidyne (CCH3), which is identified by its δ(CH3) bending mode at 1327 cm-1. The reaction mechanism for this conversion is quite complex; in the literature there are discrepancies in the identification of the intermediates with both vinyl (CHCH2) and vinylidene (CCH2) having been proposed. The experimental data available to date favors the formation of vinylidene as an intermediate in the conversion of acetylene to ethylidyne (CCH3). Evidence for vinylidene is seen in the appearance of its bending mode (δ(HCH)) at 1425 cm-1. The possible mechanism of ethylidyne (CCH3) formation is through isomerization of acetylene to vinylidene (CCH2) followed by hydrogenation of vinylidene. In the temperature range of 400 to 450 K, C2H2 decomposes and forms a CxHy species as verified by TPD spectra showing an H2 peak at 440 K following C2H2 adsorption at low temperature. The low energy electron diffraction (LEED) pattern of acetylene adsorbed at 95 K gives rise to a (√3×√3)R30∘ pattern. The experimental result is also supported by quantum mechanical computational calculations based on density functional theory.