Palladium has been introduced into the layered vanadyl hydrogen phosphate hemihydrate VOHPO4.0.5H(2)O in different ways depending upon the medium of preparation. In aqueous medium, the introduction of palladium leads to the formation of a new phase containing mixed valent vanadium whereas in the preparation in organic medium, the palladium appears to substitute into the lattice of the parent compound. The palladium-incorporated compounds have been found to be catalytically active, both for oxidative coupling as well as for hydrogenation reactions, with the activity and selectivity varying quite markedly with the mode of incorporation. (C) 2002 Elsevier Science B.V. All rights reserved.