We herein present an easy approach to increase drastically the catalytic activity of Ru/gamma-Al2O3 catalysts in ammonia decomposition by surface modification with alkali hydroxides. The best activities have been achieved by a catalyst modification with lithium hydroxide in a Li/Al ratio of 1.7. In contrast, coatings with potassium and caesium hydroxide caused mass transfer limitations in the catalytic material already at low amounts (ratios alkali/Al <0.2-0.3). MAS ssNMR and XRD studies indicate the in-situ formation of alkali aluminates resulting in a basic modification of the support. (C) 2015 Elsevier B.V. All rights reserved.