The selective hydrogenation of octanal in the presence of octene using y-alumina supported copper-silver bimetallic catalysts.
This work pertains to the selective hydrogenation of octanal in the presence of octene, which has applications in the hydroformylation process. The octanal should be hydrogenated to the desired product, octanol, while avoiding or inhibiting the hydrogenation of octene. Since octene is more thermodynamically favoured to hydrogenate, complete octene hydrogenation inhibition is difficult. This study aims to obtain a deeper understanding of the surface chemistry, which occurs on γ-alumina supported copper-silver bimetallic catalysts. This was done by first investigated monometallic copper catalyst at different weight loadings (5 and 15 wt%), then extending this to different weight loadings of the CuAg bimetallic catalysts, while maintaining the total metal loading. Additionally, the effect of the Cu-Ag metal ratios and impregnation sequence were investigated. Seven CuAg bimetallic catalysts and two Cu monometallic catalysts were synthesized via wet impregnation, and characterized using various techniques to determine surface morphology and the metal-metal and metal-support interaction on the catalyst surface. The characterization showed higher copper loadings (15 wt%) formed agglomerates. The 5 wt% catalysts showed the metals to be well dispersed, with the effect of impregnation sequence showed significant differences simultaneous impregnation and the sequential bimetallic catalysts resulting in changes to the metal dispersion and catalyst acidity. The feed used consisted of 2% octene, 10% octanal and 88% octanol. All reactions were temperature and pressure dependent, with optimum conditions of 50 bar and 160 °C. The overall result from catalytic testing showed silver to play a significant role in the selective hydrogenation of octanal in the presence of octene. The effect of impregnation sequence showed the simultaneous impregnation to give higher octanal and octene conversions, compared to the sequential impregnation catalysts, due to the synergistic effect between two metals in close contact with each other. Sequential impregnation showed that when the copper was impregnated first followed by silver, produced lower octene conversions, and hence was a more suitable catalyst system for selective hydrogenation. This research showed that γ-alumina supported CuAg catalysts are beneficial for the selective hydrogenation of octanal while in the presence of octene in a competitive reaction environment.