A comparative DFT study of the catalytic activity of the 3d transition metal sulphides surfaces

R. Gomez-Balderas a,c, R. Oviedo-Roa b , J.M. Mart ınez-Magad an b,c,*, C. Amador a , D.A. Dixon d

a Departamento de F ısica y Qu ımica Teo rica, Edif. B, Facultad de Qu ımica, UNAM, Circuito Escolar, Cd. Universitaria, Me xico D.F. 04510, Mexico

b Programa de Ingenier ıa Molecular, Instituto Mexicano del Petro leo, Eje Central La zaro Ca rdenas 152, Me xico D.F. 07730, Mexico

c Departamento de Ciencias Qu ımicas (Fisicoqu ımica), Facultad de Estudios Superiores Cuautitla n Av. 1 de Mayo S/N, Cuautitla n Izcalli, Edo. de Me xico 54740, Mexico

d William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box999, Richland, WA 99352, USA

Received 7 June 2002; accepted for publication 29 July 2002


Abstract 

The catalytic activity of the first transition metal series sulphides for hydrodesulfurization (HDS) reactions exhibits a particular behaviour when analysed as a function of the metal position in the Periodic Table. This work reports a comparative study of the electronic structure of the bulk and of the (0 0 1) metal surface (assumed to be the reactive surface) for the Sc–Zn monosulphides. The systems were modelled using the NiAs prototype crystal structure for the bulk and by applying the supercell model with seven atomic layers for the (0 0 1) surfaces. The electronic structure of closed-packed solids code based on the density-functional theory and adopting the muffin-tin approximation to the potential was employed in the calculations of the electronic properties. For the Co and Ni sulphides, the density of states (DOS) variations between the metal atom present in the bulk and the ones exposed at the surface show that at the surface, there exists a higher DOS in the occupied states region just below the Fermi level. This feature might indicate a good performance of these two metal sulphides as substrates in the HDS reactions favouring a donation, back-donation mechanism. In contrast, the DOS at the surface of Mn is increased in the unoccupied states region, just above the Fermi level. This suggests the possibility of a strong interaction with charge donating sulphur adsorbate atoms poisoning the active substrate surface.


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