Catalytic Active Sites in Molybdenum Based Catalysts

Abstract

In situ metal, acid and metal-acid (bifunctional) catalytic active functions were prepared following partial reduction by hydrogen of MoO3 deposited on TiO2 at temperatures between 623 K and 673 K. The bifunctional structure is obtained following the reduction of MoO3 to MoO2. The metallic properties of MoO2 are attributed to the delocalized p electrons above the Mo atoms place along the C-axis of the deformed rutile structure of this phase and observed as a density of states at the Fermi level. Hydrogen dissociation by this metallic function and bonding of the produced H atoms to surface oxygen atoms results in the formation of Bronsted acid Mo-OH function(s). Accordingly, a bifunctional (metal-acid) MoO2-x(OH)y structure is formed on the TiO2 support. The bifunctional properties enabled to perform isomerization reactions of light naphtha hydrocarbons into branched species of higher octane number. This catalyst is proposed as a possible replacement of the commercially used Pt deposited on chlorinated alumina catalysts in which toxic chlorine is employed and benzene is produced as a byproduct of n-hexane isomerization. The acid function in this bifunctional Mo system is quenched following the addition of controlled amount of sodium. The presence of only the metallic function in this modified NaMoTi system is monitored via the hydrogenation of olefins and enabled to define the bifunctional mechanism of the hydrocarbon isomerization process performed by MoO2-x(OH)y structure.