AVS 51st International Symposium
    Surface Science Monday Sessions
       Session SS-MoP

Paper SS-MoP21
Reactivity of Metal Carbide Surfaces and Nanoparticles: a Density Functional Study

Monday, November 15, 2004, 5:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: P. Liu, Brookhaven National Laboratory
Authors: P. Liu, Brookhaven National Laboratory
J.A. Rodriguez, Brookhaven National Laboratory
J.T. Muckerman, Brookhaven National Laboratory
Correspondent: Click to Email
The destruction of S-containing molecules is a very important issue in the chemical industry and the control of environmental pollution. The reactivity of metal carbide surfaces, M@sub2@C(001) (M=Ti,V,Mo) and MC(001), as well as M@sub8@C@sub12@ (metallocarbohedrene, metcar in short) nanoparticles towards sulfur, sulfur dioxide and thiophene was investigated using density functional theory. Our study reveals unexpected ligand and steric effects. Due to the corner or edge sites (ligand effect), the M@sub8@C@sub12@ nanoparticle behaves as active as M@sub2@C(001) towards sulfur and sulfur dioxide in spite of the high C/M ratio and C@sub2@ groups. Spontaneous S-O bond cleavage was observed on both M@sub8@C@sub12@ and M@sub2@C(001). In contrast, these adsorbates bond weakly with MC(001), and there is an activation barrier for the decomposition of SO@sub2@ on MC(001). Contrary to common assumptions, the C atoms are not simple spectators and play a key role in the energetics for the dissociation of sulfur dioxide. In the case of thiophene adsorption, only M@sub2@C(001) exhibits a high reactivity that leads to a spontaneous S-C bond cleavage. The interaction of thiophene with both MC(001) and M@sub8@C@sub12@ is weak. On the nanoparticle, steric repulsion between the C@sub2@ groups and thiophene overcomes the high reactivity of the Mo atoms in corner or edge sites (ligand effect). Our results illustrate the complex interplay of ligand and steric effects in nanoparticles of metal compounds.