Co,Al-MCM-41 catalysts with various n(Si)/(n(Co) +n(Al)) ratios were synthesized and extensively characterized by low-angle XRD, TGA/DTG, BET, AAS, DRIFT UV-Vis DRS and ESR. UV-Vis DRS and ESR studies reveal that cobalt in Co,Al-MCM-41 is highly symmetrical and occurs in tetrahedral coordination. Some of the cobalt atoms are transformed into the cobalt oxide form when n(Si)/(n(Co) + n(Al)) is increased to 20. t-Butylation of phenol with isobutanol was studied in the vapor phase as a model reaction at temperatures between 200 and 500 degreesC. The products obtained were O-tert-butyl phenol (OTBP), 2-tert-butyl phenol (2TBP) and 4-tert butyl phenol (4TBP). O-Butenyl phenol (OBP) and 2-butenyl phenol (2BP) were also observed along with normal alkylated products. The phenol conversion drastically increased with temperature over all the catalysts. The activity of the catalysts followed the order of Co,Al-MCM-41 (20) > Co,Al-MCM-41 (50) > Co,Al-MCM-41 (80) > Al-MCM-41 (23). The influences of various parameters such as temperature, reactant feed ratio and feed rate, time on stream on conversion and products selectivity were studied and the salient results are discussed. (C) 2004 Elsevier B.V. All rights reserved.