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

• Published in: Microporous and mesoporous materials Vol. 339; p. 111991
• Main Authors: Obeso–Estrella, R., Pawelec, B., Mota, N., Flores, L., Melgoza, J.M.Q., Yocupicio–Gaxiola, R.I., Zepeda, T.A.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.07.2022
• Subjects: Alumina; Crystal growth; Sulfides; Supported catalysts; Titanium oxide; Crystal growth; Supported catalysts; Sulfides; Titanium oxide; Alumina
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2022.111991

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. [Display omitted] •Titania loading influenced on the metal–support interaction and the type of titania phases.•Ti–promoted species are related to increase of the direct desulfurization route.•Non–stoichiometric titanium oxides are necessary to formation of TiCoMoS active phase.