Ferrospinels based on Co and Ni prepared via a low temperature route as efficient catalysts for the selective synthesis of o-cresol and 2,6-xylenol from phenol and methanol

The alkylation of phenol with methanol is conducted over Ni1-xCoxFe2O4 (x = 0, 0.2, 0.5, 0.8 and 1.0) type systems prepared via low temperature route. Alkylation leads to predominantly ortho methylation of phenol, yielding o-cresol and 2,6-xylenol as the products. Under optimized conditions, the total ortho selectivity was greater than or equal to94%, regardless of the catalyst composition. Only traces of anisole is formed and hardly any other xylenol or cresol isomers are detected. Phenol conversion and the individual selectivities for o-cresol and 2,6-xylenol depend strongly on the catalyst composition. Selectivity for o-cresol was maximum for NiFe2O4 (i.e., when x = 0), whereas upon progressive substitution of Co2+ ions for Ni2+ ions, the 2,6-xylenol selectivity increases with a concomitant decrease in the o-cresol selectivity. Maximum phenol conversion and 2,6-xylenol selectivity (also total ortho selectivity) were observed over CoFe2O4 (x = 1). The activity and selectivity were shown to be strongly dependent on the surface acid-base properties of the system. The influences of surface acidity, cation distribution in the spinet lattice and various reaction parameters are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.