Effect of Various Au/Al2O3 Preparations on Catalytic Behaviour during the Continuous Flow Hydrogenation of an Octanal/Octene Mixture

Abstract

AbstractSupported gold catalysts were prepared on a γ‐Al2O3 support by using the incipient wet impregnation and the deposition–precipitation methods. These catalysts were assessed for the continuous flow, liquid phase hydrogenation of an octanal/octene mixture, and their activity was compared with the activity of a commercially available Au/Al2O3 catalyst. These catalysts were characterised by inductively coupled plasma optical emission spectroscopy, hydrogen chemisorption, BET surface area and pore volume measurements, Raman spectroscopy, temperature‐programmed reduction of hydrogen, energy‐dispersive X‐ray spectroscopy mapping, HRTEM and powder XRD to determine gold crystallites. The results obtained revealed that gold crystallite size, dispersion and the presence of gold chloride had a significant effect on the product selectivity obtained. Large gold crystallites (particle size >15 nm) unevenly distributed on the alumina support obtained by using the wet impregnation method were inactive in hydrogenation. Hydrogen spillover resulted in the formation of protonic acid sites originating from molecular hydrogen, together with the formation of HCl‐catalysed acetal, and yielded 90 mol % selectivity towards the C24 acetal. In contrast, small gold crystallites (particle size <10 nm) evenly distributed on the alumina support obtained by using the deposition–precipitation preparation method facilitated the hydrogenation of the aldehyde and yielded 75 mol % selectivity towards the desired product, octanol.