Homogeneous catalysis by evaporated solids

About 10 years ago, sodium aluminate has been found as suitable catalyst for the pure dehydrogenation of methanol to anhydrous formaldehyde. At first, the reaction was supposed to follow a heterogeneous mechanism. Later on, experimental results with a special set-up were at variance. Recent investigations revealed the loss of catalytically active species from the solid aluminate into the vapour phase where the entire reaction is likely to take place. Furthermore, evaporated elemental sodium catalyses the dehydrogenation of methanal in a homogeneous vapour-phase reaction. With respect to additional investigations carried out lately, a conclusive reaction mechanism is proposed which explains both the reaction with sodium aluminate and evaporated elemental sodium as catalysts in a proper way. (C) 1999 Elsevier Science B.V. All rights reserved.