The performances of Ni-exchanged MCM-41 mesoporous material as catalyst for the ethylene oligomerization were evaluated in a pilot plant equipped with a continuous stirred tank reactor (CSTR). During the catalytic tests performed at 30 degrees C, without any start-up solvent, over 170h on stream, the catalyst was highly active and stable to deactivation. Moreover, the reaction was very selective, resulting mainly in C-4, C-6, C-8 and C-10 olefins. The CSTR unit described in this article proved to be an effective and useful tool for performing complex catalytic studies, involving three-phase systems. (C) 2011 Elsevier B.V. All rights reserved.