tert-Butylation of toluene with tert-butanol in the liquid phase was studied over large pore mordenite zeolite catalyst (H-MOR CBV 21A with Si/Al = 10.5) and over cerium-modified parent zeolite with 1-6 wt.% of cerium. The catalytic activity and para-selectivity of parent and cerium-modified H-mordenite catalysts is discussed. Non-modified H-MOR is catalytic active (66% conversion of toluene), with para-selectivity near 84% at 180 degrees C after 8 It. Cerium modification of parent mordenite by impregnation decreases catalytic activity but enhances and retains constant high para-selectivity (near 90%). Secondary reactions involved in the alkylation reaction are dealkylation of tert-butyltoluenes and isomerisation of 4-tert-butyltoluene to more stable 3-tert-butyltoluene. The positive influence of cerium modification of parent zeolite on transformation of 4-tert-butyltoluene was investigated. It was proved by Xe-129 NMR spectroscopy that cerium/ceria is located on the external surface of H-mordenite, not inside the main channels. It was confirmed by XRD that after calcination at 500 degrees C in the flow of dry air cerium is in the form of cerium/ceria. tert-Butylation of toluene with tert-butanol over shape-selective mordenite catalysts can be an ecofriendly process for industrial preparation of 4-tert-butyltoluene which is important intermediate product for fine chemicals. (c) 2005 Elsevier B.V. All rights reserved.