Selective production of orthoalkyl phenols on Cu_0.5Co_0.5Fe₂O₄: a study of catalysis and characterization

Abstract

Phenol alkylation was carried out on Cu_1-xCo_xFe₂O₄ (x = 0-1) by employing various alkylating agents: CH₃OH, CH₃OCOOCH₃ dimethyl carbonate (DMC), C₂H₅OH, 2-C₃H₇OH and isobutene (IB), under a wide variety of reaction conditions; a comparative analysis is made. Cu_0.5Co_0.5Fe₂O₄ displays the highest phenol alkylation activity, irrespective of the alkylating agents. The catalytic conversion of phenol follows the following order: MeOH ≈ DMC > EtOH > isopropanol ≈ IB. Ortho-dialkylated product formation decreases as the chain length of alkylating agent increases. X-ray photoelectron spectra (XPS) and Auger electron spectroscopy analysis of fresh and spent Cu_0.5Co_0.5Fe₂O₄ catalysts revealed a partial reduction of metal ions due to reaction. Valence band studies reveal an increase in the overlap of metal ion 3d bands from fresh to spent catalysts due to a large decrease in the energy gap between them. The high activity observed is attributed to an optimum distribution of Cu-species with hetero-atom neighbors on the surface and a large overlap between the Cu and Co 3d bands. A mechanism involving the reaction of phenol and alcohol molecules adsorbed simultaneously on the same acid-base pair site is supported by IR spectroscopy results from the reactants and pyridine adsorbed on catalyst.