Active Sites and Influence of Real Structure of Gold Catalysts in the Selective Hydrogenation of Acrolein to Allyl Alcohol

We have successfully employed oxide supported gold catalysts in the gas-phase hydrogenation of acrolein, the ,-unsaturated aldehyde being most difficult to hydrogenate at the carbonyl group. The relation of structural characteristics and surface state of these catalysts with respect to their actiity and selectiity hae been studied by surface analytical techniques and high-resolution transmission electron microscopy which was carried out to elucidate the real crystal structures of gold particles. The performance of gold catalysts formed by arious preparation and pretreatment procedures was strongly dependent on the reduction time: Increasing the latter resulted in a high number of multiple twinned gold particles which decrease both the selectiity to the desired product, allyl alcohol, and the turnoer frequency. Furthermore, it has been demonstrated for the first time that the addition of a second metal (indium) results in a selectie decoration of the faces of nanosized gold particles leaing edges free. The actie sites of supported gold catalysts, faoring the adsorption of C=O group of acrolein and subsequent reaction to allyl alcohol, hae been identified as edges of gold nanoparticles. The zinc oxide supported bimetallic Au-In catalyst produced allyl alcohol with a selectiity of 63% which is comparable to the best hydrogenation catalysts for this reaction