Alkylation of biphenyl with propene in mesitylene as a solvent over a series of modified mordenite catalysts was studied in a continuous microflow reactor. Na-mordenite was modified by subjecting it to combinations of acid extraction and calcinations. Performance and selectivity for 4,4’-diisopropyl biphenyl formation of the mordenite catalysts depended on their Na content, Si/Al ratio and porous texture. Best results were obtained using a highly crystalline modified mordenite having a low sodium content, a Si/Al ratio of about 70, a secondary pore volume in mesopores of about 0.15 ml/g and a surface area in mesopores of about 30 m(2)/g. Thermal analysis showed that coke on deactivated catalysts consisted mainly of propene oligomers.