Chemisorption of acetylene and ethylene on Rh(111): A low energy electron diffraction (LEED), high resolution electron energy loss (ELS), and thermal desorption mass spectrometry (TDS) study

Journal Article · Thu May 01 04:00:00 EDT 1980 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.439760· OSTI ID:5481670

Dubois, L H; Castner, D G; Somorjai, G A

We report the results of a detailed investigation of the chemisorption and reactivity of acetylene (C/sub 2/H/sub 2/) and ethylene (C/sub 2/H/sub 4/) on the Rh(111) single crystal surface. Below 270 K ELS measurements indicate that acetylene chemisorbs on Rh(111) with its C--C bond oriented parallel to the surface forming an approximately sp/sup 2/ hybridized species. LEED investigations show that both C/sub 2/H/sub 2/ and C/sub 2/H/sub 4/ form metastable (2 x 2) surface structures on Rh(111) below 270 K. An irreversible order--order transformation occurs between 270 and 300 K to a stable c(4 x 2) hydrocarbon overlayer. The stable species formed from both molecules are identical. Hydrogen addition to chemisorbed acetylene is necessary to complete this conversion. The geometry of the adsorbed ethylene species does not change during this transformation although the overlayer structure does. This stable hydrocarbon species is identical to the hydrocarbon species formed from the chemisorption of either C/sub 2/H/sub 4/ or C/sub 2/H/sub 4/ and hydrogen on Pt(111) above 300 K. The addition of H/sub 2/ to chemisorbed C/sub 2/D/sub 2/ or C/sub 2/D/sub 4/ results in H--D exchange, but no change in the adsorbate geometry is detected by ELS. Decomposition of these molecules occurs on the Rh(111) surface above approx.420 K.

• Research Organization: Materials and Molecular Research Division, Lawrence Berkeley Laboratory, and Department of Chemistry, University of California, Berkeley, California 94720
• OSTI ID: 5481670
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 72:9; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640300* -- Atomic
Molecular & Chemical Physics
74 ATOMIC AND MOLECULAR PHYSICS
ACETYLENE
ALKENES
ALKYNES
CHEMICAL REACTIONS
CHEMISORPTION
COHERENT SCATTERING
DIFFRACTION
ELECTRON DIFFRACTION
ELEMENTS
ETHYLENE
HYDROCARBONS
MASS SPECTROSCOPY
METALS
ORGANIC COMPOUNDS
PLATINUM METALS
REFRACTORY METALS
RHODIUM
SCATTERING
SEPARATION PROCESSES
SORPTION
SORPTIVE PROPERTIES
SPECTROSCOPY
SURFACE PROPERTIES
SURFACES
TRANSITION ELEMENTS