Tungsten containing TUD-1 catalysts with Si/W ratios of 10-50 were synthesised by a two-step impregnation method and a direct one-step sol-gel method. The one-step method yielded finely dispersed catalytically active tungsten oxide nano-particles (<1 nm) (at Si/W ratio above 20), while the two-step method yielded both tungsten oxide nano-particles and bulk tungsten oxide. This was established using INAA, N-2 physisorption, powder XRD, Raman spectroscopy, TEM, diffuse reflectance UV-vis, FT-IR, H-2-TPR and NH3-TPD analysis. Both types of catalyst preparation resulted in active acidic catalysts for the Prins cyclisation of citronellal. It was demonstrated that the finely dispersed tungsten oxide nano-particles were responsible for the catalytic activity. (C) 2013 Elsevier B.V. All rights reserved.