Geochemistry and catalysts preparation: alumina as a chemical reactant in the synthesis of MoO_x/Al_2O_3 and WO_x/Al_2O_3 systems

摘要

This study deals with the role of alumina dissolution on the speciation of Mo during the synthesis of MoO_x/Al_2O_3 catalysts. Alumina dissolution leads to the formation of an aluminomolybdic species in solution and its deposition on the support. These phenomena, explained by using concepts developed in geochemistry, can have general implication in catalyst synthesis since the formation of mixed species is also shown to occur for WO_x/Al_2O_3 preparation. Depending on the preparation method, these mixed species are either molecularly dispersed or precipitated as a 3D phase on the support. The influence of such species on the state of the catalyst obtaiend after calcination is discussed.