The influence of potassium on the structure and properties of titania-supported vanadium oxide catalysts has been studied by DFT calculations and measured experimentally by in situ temperature-programmed Raman (TP-Raman) spectroscopy and temperature-programmed reduction (TPR). Below monolayer coverage, potassium coordinates to surface vanadium oxide species altering its structure but it does not form bulk compounds. Theory and experiments agree on the weakening of the terminal V=O bond due to the interaction between potassium and vanadium oxide. K-doped vanadia-titania catalysts show a decrease of reducibility with K loading in line with the decrease in the calculated hydrogen adsorption energy for K-doped models. (c) 2007 Elsevier B.V. All rights reserved.