Amorphous zirconium, tin, titanium, vanadyl, cerium and scandium/zirconium phosphates have been evaluated in relation to their effects on the catalysed formation of peroxyacetic acid (PAA) from hydrogen peroxide and acetic acid. The rate of formation of PAA remained almost the same whether the phosphates were present or absent, for most of the phosphates. However, by exchanging the acidic hydroxyl centres in ZrPA with scandium(III), it was found that the resulting solid, ScZrPA, strongly accelerated the formation of PAA, even more so than the scandium(III) ions in homogeneous solution. (C) 2002 Elsevier Science B.V. All rights reserved.