Insight into the Correlation between Cu Species Evolution and Ethanol Selectivity in the Direct Ethanol Synthesis from CO Hydrogenation

Graphical Tuning selectivity : Cu/SiO 2 was prepared by ammonia evaporation and used as catalyst for the direct synthesis of ethanol from CO hydrogenation. Both the Cu + /(Cu + +Cu 0 ) values and copper crystallite sizes had significant effects on the selectivity towards ethanol. Cu/SiO 2 catalyst was prepared by the ammonia evaporation method for the direct synthesis of ethanol from CO hydrogenation. The catalyst exhibited the initial ethanol selectivity as high as 40.0 wt %, which dramatically decreased from 40.0 to 9.6 wt % on the stream of 50 h. XRD, XPS, TEM and N 2 O titration techniques were employed to elucidate the ethanol selectivity change and catalyst structure evolution during reaction process. The experiment and characterization results indicated that both Cu + /(Cu + +Cu 0 ) value and copper crystallite size had great effects on the ethanol selectivity. During the initial 38 h, the ethanol selectivity obviously decreased from 40.0 to 18.2 wt %, and Cu + /(Cu + +Cu 0 ) value on the catalyst surface rapidly dropped from 0.67 to 0.39, while the copper crystallite size remained almost unchanged. However, during the reaction period of 38–50 h, the Cu + /(Cu + +Cu 0 ) value possessed no distinct change, but a further decrease in ethanol selectivity and a rapid aggregation in Cu particles were observed simultaneously. The present systematic investigation demonstrated that the decrease of Cu + /(Cu + +Cu 0 ) value was the main factor for the loss of ethanol selectivity during the initial 38 h, whereas the rapid growth of Cu particles during the reaction period of 38–50 h were mainly contributed to the further decline of ethanol selectivity.