A solid acid of tungsten-niobium oxide was obtained by evaporating the water from a mixed solution of ammonium metatungstate and niobium ammonium oxalate in water in the ratio 7:1 of W to Nb, followed by calcining in air at 400 degrees C. The catalytic activity of the solid acid for decompositions of toluene, ethylbenzene, and cumene was higher than those of tungstated zirconia, mordenite, and silica-alumina. The chief ingredient of Nb in the mixture was less effective. The acid strength was estimated by the heat of Ar adsorption to be 18.1 kJ mol(-1), the value being coincident with that of H-mordenite (18.3 kJ mol(-1)). (C) 2006 Elsevier B.V. All rights reserved.