Layered-type tungsten and tantalum oxides (W-Ta-O) were synthesized by the hydrothermal method. The synthesized W-Ta-O showed characteristic peaks at 2 theta = 22.7 degrees and 46.2 in an X-ray diffraction pattern (Cu K alpha), indicating linear corner sharing of MO6 (M = W, Ta) octahedra in the c-direction. The same layered-type materials were obtained with a wide range of W and Ta composition ratios using soluble Lindqvist-type tantalum polyoxometalate (Na-8(Ta6O19)center dot 24.5H(2)O). Na+ cations of as-synthesized W-Ta-O were replaced with NH4+ and then calcined at 500 degrees C to form Bronsted acid sites. The catalytic activity of W-Ta-O increased with increasing W ratio, suggesting that strong acid sites were generated. From Raman and adsorption measurements of W-Ta-O with various crystalline structures, it was revealed that the crystalline motif of W-Ta-O in the a-b plane was an interconnection of MO6 (M = W, Ta) octahedra and (M6O21) pentagonal units and micropore channels, but without long-range order. (C) 2016 Elsevier Inc. All rights reserved.