The present invention relates to a process for the preparation of 2,6-di-tert-butyl phenol by reacting phenol with isobutylene in presence of an aluminum phenoxide catalyst, comprising i) preparing an aluminum phenoxide catalyst and phenol comprising mixture a) by mix-ing aluminum metal with phenol, and activating the catalyst by heating the mixture to a temperature of 100 to 180° C., and ii) carrying out a reaction b) by reacting mixture a) with an isobutylene comprising stream comprising 20 to 90% by weight of isobutylene and 10 to 80% by weight of 1-butene and/or 2-butene, which reaction is carried out under pressure and the maximum pressure is 5 to 20 bar.