The kinetics and mechanism of ethylamine synthesis from ammonia and ethanol over several large pore acid catalysts are described. Mordenite produced higher monoethylamine yields than the zeolites beta, Y, mazzite, and amorphous silica-alumina. The reaction proceeds via the initial formation of ethylammonium ions, and alkylamines desorb with the assistance of ammonia and equilibrate with other ethylammonium ions before leaving the catalyst pores. The high yields of ethylamines with mordenite are related to the high acid strength of the catalyst stabilizing (alkyl)ammonium ions and so blocking the dehydration of ethanol. By choosing high ammonia partial pressures, reaction temperatures below 573 K (minimizing ethene elimination from ethylammonium ions), and subtle modifications of the parent mordenite material (EDTA leaching, silylation of the external surface) ethene selectivity was further decreased. These measures allowed us to prepare a catalyst on the basis of mordenite with a Si/Al ratio of 5 that showed 99% selectivity to ethyl amines at 60% conversion and that was stable for long times on stream.