Balancing acidity and basicity for highly selective and stable modified MgO catalysts in the alkylation of phenol with methanol

Abstract

The alkylation of phenol was investigated over magnesium oxide catalysts modified with the addition of small amount of vanadium, manganese or other components. The catalytic performance was strongly dependent on the kinds of dopants due to changes in the acid-base properties. The modified MgO catalysts showed an activity higher than pure MgO catalyst. V-Mn-MgO catalyst was found to be mon active and selective than that of V-Mgo or Mn-MgO catalyst for 2,6-xylenol. Among the modified catalysts, V-Mn-MgO catalyst was excellent in both phenol conversion and the selectivity to 2,6-xylenol. The alkylation of phenol in or ortho position was explained in the acid-base property of mixed oxide. Phenol conversion and 2,6-xylenol selectivity increased with acidity, whereas the selectivity too-cresol decreased because of the nature of the series reaction (phenol --> o-cresol --> 2,6-xylenol --> 2,4,6-trimethyl phenol (2,4,6-TMP)). Na-Mn-MgO catalyst prepared to achieve a balance between acidity and basicity was not deactivated and highly selective to o-cresol and 2,6-xylenol. Reaction temperature, feed composition and space velocity also significantly influenced the conversion and the selectivity in the alkylation of phenol. (C) 2000 Elsevier Science B.V. All rights reserved.