Molybdena deposited on titania by equilibrium deposition filtration: structural evolution of oxomolybdenum() sites with temperature

The equilibrium deposition filtration (EDF) method, an advanced catalyst synthesis route that is based on a molecular level approach, can be used for tailoring the oxometallic phase deposited on a porous oxide support. Here, the EDF method is used for synthesizing (MoO x ) n /TiO 2 catalysts. In situ Raman spectroscopy in the temperature range of 25450 C, low temperature (77 K) EPR spectroscopy and DR-UV spectroscopy are used for studying the evolution of the structural configuration of oxoMo VI species on TiO 2 with increasing temperature as well as the influence of the supported (MoO x ) n species on the photo-generation of electrons and holes of TiO 2 . This study concerns (MoO x ) n /TiO 2 samples in which the surface densities after calcination are 0.3, 2.6 and 3.9 Mo per nm 2 , thereby covering a very wide range of submonolayer coverage. The gradual heat treatment of the catalysts results in a transformation of the initially (prior to drying) deposited species and the pertinent species evolution at the nano-level is discussed by means of a number of mechanisms including anchoring, association, cleavage and surface diffusion. The temperature evolution of the Mo( vi )oxo species structures in molybdena/titania catalysts is studied from the wet (prior to drying) to the final calcined catalyst state.