EFFECT OF SUBSTITUTION OF FE3+ CR3+ ON THE ALKYLATION OF PHENOL WITH METHANOL OVER MAGNESIUM-ALUMINUM CALCINED HYDROTALCITE/

Hydrotalcite (HT)-like compounds with the general formula, Mg0.8M(III) (0.2)(OH)(2)(CO3)(0.1).yH(2)O with M(III)=Al, Fe and Cr (Mg/Al atomic ratio 4) were synthesized by coprecipitation method using a mixture of NaOH/Na2CO3 as precipitant. The Powder X-ray diffraction (PXRD) of al uminium and iron containing samples (M(III)=Al, Fe) showed single phas e corresponding to HT when a mixture of HT and MgCrO4 . 7H(2)O phase w as detected for chromium containing sample (M(III)=Cr). These samples after calcination at 450 degrees C/8 h/air, were used as catalyst for vapour phase alkylation of phenol with methanol. MgAl 4.0-CHT showed n early 100% phenol conversion around 400 degrees C and the reaction was found to proceed predominantly through the formation of anisole (O-al kylation). Isomorphous substitution of Al3+ by Fe3+ or Cr3+ in the HT framework resulted in a decrease in phenol conversion in the order MgA l 4.0-CHT>MgCr.0-CHT>MgFe 4.0-CHT and the alkylation reaction was foun d to proceed exclusively at C-centres (C-alkylation) to give o-cresol as a major product. The catalytic performance for the methylation of p henol has been correlated with acid-base properties of the catalysts a s determined by test reactions such as decomposition of 2-methyl-3-but yne-2-ol (MBOH) and cyclohexanol. (C) 1997 Elsevier Science B.V.