Perovskites and metal nitrides as catalysts in the base-catalysed aldol addition of isobutyraldehyde to formaldehyde†
Hydroxypivaldehyde represents an important intermediate in the production of neopentyl glycol, which in turn is widely applied in the production of e.g. polyesters, plasticizers, synthetic resin paints and lubricants. It is industrially produced via aldol addition of isobutyraldehyde to formaldehyde catalysed by homogeneous bases. However, the major disadvantages include the difficult separation of the base from the product stream, the formation of salts upon neutralisation and side reactions as well as the catalyst's hazard potential due to corrosion, toxicity and inflammability. A set of perovskites and metal nitrides were investigated as solid catalysts for aldol reactions establishing structure–performance correlations. For perovskites, a correlation of the catalytic activity and the degree of distortion as well as the presence of other phases is found but the most promising catalyst, BaZrO3, shows deactivation in recycling experiments. Amongst the metal nitrides, AlN exhibits high activity and stability in batch recycling experiments. Transferring the system into a continuous fixed bed reactor reveals high stability over 150 h time on stream at 423 K. XRD and SEM/EDX confirm the formation of boehmite caused by the hydrolysis of AlN in an aqueous reaction medium. This transformation is associated with a significant increase in the basicity and acidity of the material, which is proposed to account for its high catalytic activity.