AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP2
Substrate-Dependent Interaction of Carbon Monoxide and Ammonia on Metal Carbide Surfaces

Wednesday, October 4, 2000, 11:00 am, Room Exhibit Hall C & D

Session: Poster Session
Presenter: L.C. Fernández-Torres, University of Houston
Authors: S.S. Perry, University of Houston
L.C. Fernández-Torres, University of Houston
R.L. Guenard, University of Houston
O. El-bjeirami, University of Houston
S.V. Didziulis, The Aerospace Corporation
P.P. Frantz, The Aerospace Corporation
Correspondent: Click to Email
A study of the interaction of carbon monoxide (CO) and ammonia (NH@sub 3@) with titanium carbide (TiC) and vanadium carbide (VC) is presented. The interaction of CO and NH@sub 3@ with the (100) face of the single crystal carbides was studied over the temperature range of 100-400 K. The adsorption states of CO and NH@sub 3@ were probed with high resolution electron energy loss spectroscopy (HREELS) and photoelectron spectroscopy. The desorption of CO and NH@sub 3@ was followed with temperature programmed desorption (TPD). Together, these measurements indicate that both CO and NH@sub 3@ adsorb molecularly on TiC and VC. However, HREELS measurements show CO adsorbs more strongly on VC than on TiC, and NH@sub 3@ adsorbs similarly on TiC and VC. TPD supports these observations; CO has a higher desorption temperature on VC than on TiC while NH@sub 3@ has a similar desorption temperature from the two surfaces. Strong evidence of @pi@-backbonding for CO on VC is seen in the vibrational data, as well as in the core and valence level photoelectron spectra. This mechanism, which is not active on TiC, differentiates the interaction of CO with these two substrates. Similar interaction mechanisms and adsorption energies are observed for NH@sub 3@ on TiC and VC, where @pi@-backbonding would not be expected to play a role. These results are discussed in terms of the difference in electronic structure between the two metal carbides.