Ru and Ag promoted Co/Al2O3 catalysts for the gas-phase amination of aliphatic alcohols with ammonia†
The present paper describes the synthesis of primary amines from long-chain aliphatic alcohols and ammonia using alumina-supported noble metal doped cobalt formulations with moderate cobalt loading (5 wt%). The influence of the noble metal nature, loading and impregnation sequence was studied in detail and comprehensively characterized using XRD, H2-TPR, CO-TPD and STEM-EELS/EDS. While all noble metals exerted a positive effect on the cobalt reducibility, Ag and Ru impacted to a higher extent the activity and selectivity for amine synthesis. The impregnation protocol was found to be critical with the best results being obtained for sequentially impregnated Ag–Co and co-impregnated Co(Ru) catalysts. Further optimization of the Ag and Ru metal loading led to two formulations affording a comparable activity to that of an alumina-supported catalyst containing 2.4 times more Co. At optimized conditions, the best formulation (5 wt% Co, 3 atom% Ag) afforded 90% conversion and 78% yield to 1-octylamine in the gas-phase amination reaction of 1-octanol with ammonia at 200 °C using 21 equiv. of ammonia compared to 1-octanol, which overcomes the maximum reported yield on benchmark Ni-alumina formulations (70%). Furthermore, this formulation showed high stability for at least 6 h on stream. A survey of the effect of the reaction variables on the catalytic performance revealed a co-catalytic effect of Ag, impacting positively both the activity and selectivity.