Oxidation of 2,3,6-trimethylphenol over Ti- and V-containing mesoporous mesophase catalysts: Structure-activity/selectivity correlation

The oxidation of 2,3,6-trimethylphenol (TMP) has been carried out over well-organized Ti- and V-containing mesoporous mesophase silicate catalysts (Ti- and V-MMM) using hydrogen peroxide and tert-butyl hydroperoxide (TBHP) as oxidants. Vanadium leaching was observed in the V-MMM/H2O2 and V-MMM/TBHP systems, whereas no titanium leaching occurred for Ti-MMM with both oxidants. TMP oxidation runs on a surface of Ti-MMM catalyst, producing 2,3,5-trimethyl-1,4-benzoquinone (TMBQ) with selectivity as high as 86% at 100% TMP conversion. Titanium content in Ti-MMM determines the state of the active catalytic site and influences the structure regularity, thus affecting the catalytic behavior. The catalysts with titanium loading in the 1.5-2 wt% range show the highest activity and selectivity. Some loss of catalytic properties observed after recycling may occur due to collapsing of the catalyst structure caused by water. The lower the water concentration in the reaction mixture, the more stable the catalyst. (C) 2001 Academic Press.