A semiempirical theoretical study of Ni/Al2O3 and Ni-Sn/Al2O3 catalysts for CH4 reforming

FERREIRA MARÍA LUJÁN; NORA NICHIO; OSMAR FERRETTI

JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2003 vol. 202 p. 197 - 213

1381-1169

In order to investigate the nature of Ni supported on -Al2O3 and its modification with Sn in methane reforming reactions,a theoretical study was carried out. A molecular orbital approach of the extended Hückel type was performed to obtain theformation energies of postulated adsorbed and reacted species of CH4, H2O, O2 and CO2 on a model of Ni and NiSn surfacesresembling Ni/-Al2O3 and NiSn/-Al2O3. Three different known planes of fcc Ni were considered: (1 1 1), (0 0 1) and(1 1 0). Possible adsorbed and reacted species of CH4, H2O, O2 and CO2 on Ni with Ni all around, Sn fully rounded byNi and Ni near a Sn were discussed using reaction energies. The interaction NiSn in Ni clusters has been claimed to be ofinterstitial substitution-type in alloys. The (1 1 1) plane is the most reactive for adsorption. In agreement with experimentalwork, methane activation on Ni is the controlling step in reforming of methane with CO2 (R), partial oxidation with O2 (POM)and mixed reforming using CO2 and O2 (MR). Sn near a Ni changed the adsorption properties of it. Favoured reactions for Snrounded by Ni on (0 0 1) and (1 1 1) planes are the adsorption of CO2 and formation of a Sn?CO bond and the generation ofSn?H bonds from methane and water dissociation. The theoretical results are discussed in the context of previously publishedexperimental data.