A Study of Catalysis by Metal Phosphates. IV. The Alkylation of Phenol with Methanol over Metal Phosphate Catalysts

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Abstract
The catalytic methylation in the vapor phase over various metal phosphates has been investigated using a conventional flow reactor at temperatures ranging from 350 to 500 °C under atmospheric pressure. The Ca3(PO4)2 catalyst was excellent in both its activity and its selectivity for ortho-methylation, giving predominantly o-cresol and 2,6-xylenol, whereas the BPO4 or CaHPO4 catalyst simultaneously promoted the formation of anisole. The activity of Ca3(PO4)2 was significantly higher than that of the CaO or MgO catalyst. The influences of the reaction temperature, the contact time, and the calcination temperature of the catalyst upon the conversion of phenol, and the yields of the products were investigated in detail over the Ca3(PO4)2 catalyst. The activities and the selectivities of various catalysts were discussed in connection with their acid-base properties. The mechanism of the participation of both the acidic and basic sites in the methylation was also discussed.