Applied Catalysis A: General, Vol.273, No.1-2, 35-45, 2004
Selective production of orthoalkyl phenols on Cu0.5Co0.5Fe2O4: a study of catalysis and characterization
Phenol alkylation was carried out on Cu1-xCoxFe2O4 (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. Cu0.5Co0.5Fe2O4 displays the highest phenol alkylation activity, irrespective of the alkylating agents. The catalytic conversion of phenol follows the following order: MeOH approximate to DMC > EtOH > isopropanol approximate to 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 CU0.5Co0.5Fe2O4 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. (C) 2004 Elsevier B.V. All rights reserved.
Keywords:phenol;ortho-alkylation;ferrite;XPS;copper oxide;cobalt oxide;surface composition;2,6-xylenol;2-ethyl phenol;reaction mechanism