This invention relates to a process for pretreating a zeolite catalyst, specifically a zeolite which has been modified with phosphorus. The catalyst may be used in a process for alkylation of aromatics, specifically toluene methylation. The pretreatment is first to contact the catalyst with the process reactants used in a process for alkylation of aromatics for at least two hours at conditions to produce an alkylated aromatic product and then with a gaseous stream containing oxygen at a temperature and for a time until there is no oxygen consumption. The zeolite may be a MFI zeolite. This pretreatment procedure for a phosphorus-modified zeolite catalyst produces a catalyst which has increased run time, i.e., decreased deactivation rate, compared to a fresh catalyst, even after successive regenerations.