The preparation and characterisation of Fe-promoted Al₂O₃-supported Rh catalysts for the selective production of ethanol from syngas

This paper describes the development of a selective alumina-supported rhodium catalyst for the synthesis of ethanol from high pressure (10 bar) CO/H₂ mixtures. It has been shown that selectivity to ethanol of up to 50% can be achieved with an alumina-supported Rh catalyst containing 2 wt% Rh and promoted by 10 wt% Fe. Characterisation of the Fe-promoted Al₂O₃-supported Rh catalysts with increasing promoter loadings by selective chemisorption and temperature-programmed reduction (TPR) has provided evidence of a close interaction between the active metal and the promoter oxide especially at higher promoter loadings. The results obtained are consistent with the buildup of a close packed monolayer of the promoter oxide on the support surface which is possible due to the presence of a high surface density of hydroxyl groups on alumina. The influence of the metal precursor and the drying rate on the final metal salt distribution through the pore structure of a preshaped alumina support has also been investigated. It has been shown that impregnation of 1/16″ γ-alumina extrudates with an aqueous solution of iron nitrate causes the iron salt to be deposited at the outer edge of the pore structure. A more uniform distribution can be obtained if a methanolic solution of Fe(NO₃)₃ or an aqueous solution of an organometallic complex is used as the deposited metal precursor.