Our previous study on the o-xylene hydroisomerization over HMS-Ti modified with Ga demonstrated that R428 upon hydrogenation at atmospheric pressure the reaction proceeds exclusively via intramolecular mechanism (formation of m- and p-xylenes) and hydrogenation of benzene aromatic ring of o-, p- and m-xylenes did not occur . Thus, we consider of interest to study the effect of hydrogen pressure on the reaction mechanism over Ga2O3/HMS-Ti systems. The structural and surface properties of the synthetized catalysts were evaluated by means of different characterization techniques in order to obtain catalyst activity–structure correlation.
2.1. Catalyst preparation
The HMS-Ti substrate was synthetized according to a procedure reported by Gontier and Tuel  using neutral primary amine (dodecylamine: C12H25NH2, Aldrich 98%) as surfactant and a neutral tetraethylorthosilicate (TEOS, Si(OC2H5)4, 98% Acros) as inorganic precursor of silica. Mesitylene (C9H12, Aldrich 98%) and titanium(IV) butoxide (Aldrich 97%) were used as swelling agent and precursor of Ti4+ cations, respectively. The HMS-Ti material was prepared with a Si/Ti molar ratio of 40, which was demonstrated to be optimized Si/Ti molar ratio for HMS-Ti systems . After filtration and washing the solid with distilled water, the solid was dried at room temperature for 24 h followed by drying at 103 °C for 2 h. Finally, the solid was calcined at 550 °C for 3.5 h with a heating rate of 2.5 °C min−1.