Acidic cesium salts CSxH3-xPW12O40 have been prepared by grinding together amounts of H3PW12O40 and porous Cs3PW12O40 compounds in varying stoichiometries. It is shown that this procedure leads to a dispersion of the acid on top of the high surface area Cs3PW12O40 Salt (160 m(2) g(-1)), and, subsequently, yields high surface area materials which exhibit a much higher catalytic activity for n-butane isomerisation at 473 K when compared with samples prepared directly by chemical precipitation. This improvement holds particularly true with low Cs content (x < 2).