Impact of the impregnation sequence on the surface characteristics on Cu-Ag supported on γ-Alumina towards the liquid phase competitive hydrogenation of octanal in the presence of octene

Abstract Bimetallic Cu-Ag/Al2O3 catalysts were prepared for competitive hydrogenation of octanal to octanol, with octene as a competing reactant. These catalysts were prepared using simultaneous and sequential impregnation to determine the promotional effect of silver on the copper catalysts. The increased catalytic performance of the simultaneous impregnated 4.5Cu-0.5Ag/γ-Al2O3 (4.5 wt% Cu and 0.5 wt% Ag) catalyst included a higher octene conversion compared to the sequential catalysts which was due to the differences in synergistic copper-silver interaction. The catalysts yielded selectively high octanal and low octene conversions. It was found that under the same operating conditions at 140°C and 50 bar H2, the sequentially impregnated catalyst, S-0.5Ag-4.5Cu/γ-Al2O3 gave a high conversion of 83 %, while maintaining a low octene conversion of 4 mol%, compared to its monometallic counterpart 5Cu (5 wt% Cu/γ-Al2O3) which gave 69 % octanal conversion and 3 % octene conversion. Silver, initially used as a reduction promoter, showed to have also played a role as a structural promoter in some catalysts, which improved carbonyl adsorption as shown from the improved preferential selectivity towards octanal conversion compared to the undesired octene conversion.