Selective tert-butylation of phenol over molybdate- and tungstate-promoted zirconia catalysts

Abstract

Abstract The catalytic performance of molybdate- and tungstate-promoted zirconia catalysts for tert -butylation of phenol with tert -butanol as alkylating agent has been investigated. The reaction was carried out at 433–493 K in a fixed bed micro-reactor at normal atmospheric pressure. The promoted zirconia catalysts were synthesized by immersing the finely powdered hydrous zirconium hydroxide in aqueous ammonium heptamolybdate or ammonium metatungstate solution and subsequent oven drying and calcination at 923 K. The hydrous Zr(OH) 4 was prepared from aqueous zirconium oxychloride by hydrolysis with a dilute aqueous ammonia solution. To investigate the structural and textural properties, we characterized the synthesized catalysts by X-ray powder diffraction (XRD), BET surface area, temperature programmed reduction (TPR), temperature programmed desorption (TPD) of ammonia, scanning electron microscopy (SEM), Raman spectroscopy (RS), and FT-infrared spectroscopy (FTIR) techniques. All the characterization results reveal that the incorporated promoter cations show a significant influence on the surface and bulk properties of the ZrO 2 . In particular, the impregnated cations stabilize the metastable tetragonal phase of zirconia at ambient conditions and enhance the total number and the strength of the acid sites. A good substrate (phenol) conversion and excellent product selectivity were obtained over the promoted zirconia catalysts.