Elucidating the mechanisms of titanium–induced morphological and structural changes in catalysts on mesoporous Al2O3–TiOx mixed oxides: Effect of non–stoichiometric TiOx phase

In the present work, mesoporous Al2O3–TiOx composites with different titania loadings (4, 8 and 12 wt%) were synthesized to evaluate the effect of non-stoichiometric TiOx phases on the hydrodesulfurization (HDS) ability of the CoMo/Al2O3–TiOx catalysts. The activity of the catalysts was evaluated in the dibenzothiophene (DBT) HDS reaction carried out at 593 K, 5.5 MPa in a batch reactor. Regardless of the TiOx content, all sulfided CoMo Al2O3–TiOx catalysts were more active than the CoMo/Al2O3 catalyst. For all catalysts, DBT HDS occurs mainly through the direct desulfurization (DDS) pathway (95–97% selectivity). The most active catalysts (CoMo-12 and CoMo-4) showed evidence of the presence of non-stoichiometric titanium oxides. The synthesized materials were characterized in depth to evaluate their crystallinity, textural and morphological properties, elemental composition and acidity. Their characterization showed that: (i), the Al2O3–TiOx interaction increased with decreasing TiOx content; (ii) the strong interaction between TiOx particles and alumina led to the formation of more defined TiOx structures; (iii), an increase in titania content led to the growth of TiOx crystals along the [101] direction (relative to the [001] direction), which in turn, led to the different TiOx morphologies: nanorods → nanotubes → U-shaped nanotubes. The TiCoMoS phase can be formed if the process is performed on Ti3O5 instead of TiO2.