Role of non-stoichiometry and soft chemistry in the preparation of advanced catalysts

The role of non-stoichiometry and soft chemistry in the preparation of adva nced catalysts is discussed analysing some relevant examples of (i) differe nt classes of catalytic materials based on complex oxides (spinel-, perovsk ite-, rutile-, and scheelite-type structures) after a brief introduction on the role of solid-state and non-stoichiometry for the synthesis of new mat erials and (ii) soft routes for the preparation of mixed oxides (topochemic al reactions, intercalation, sol-gel-methods). It is shown that the catalyt ic behaviour is often associated with the presence of a defect structure in which non-stoichiometry alters bulk and surface properties creating new st ructural geometries or stabilizing unusual coordination or valence states o f metal ions. The creation of these functional properties is strictly relat ed to the possibility of synthesis by soft chemistry routes.