The active site of syngas conversion into ethanol over Cu/ZnO/Al2O3 ternary catalysts in slurry bed

Abstract

As a promising technology, selective conversion of syngas to ethanol over the CuZnAl catalyst has a long-standing interest in current energy research. Here, we report cooperative ZnO and Al2O3 clusters on the Cu(1 1 1) surface for selective hydrogenation of CO to ethanol using density functional theory (DFT) and microkinetic model. Our results show that the Cu-ZnO synergy facilitates CO initial activation to CHO, the cooperation of the three components is necessary for CH3 formation via the direct dissociation of the formed CH3OH that is the rate-controlling step throughout the whole process, and the aid of the Cu-Al2O3 synergy is indispensable for the initial carbon chain formation by CO insertion into CH3 intermediate with a 0.45 activation barrier. Apart from the ethanol synthesis, we propose the possibility of syngas conversion into ethylene glycol that is a typical atom economic reaction. Moreover, thermodynamic and kinetic barriers and charge analyses results identify that the carbon chain growth via CHO coupling with the assistant of Cu-ZnO synergy is facile for the formation of ethylene glycol. In order to achieve high ethanol productivity and selectivity over the CuZnAl catalyst, the aid of a metal promoter with the function of facilitating the CHO hydrogenation and/or suppressing the CHO coupling is required. This work not only clarifies the synergy of Cu, ZnO, and Al2O3 components of CuZnAl catalyst for ethanol synthesis, but also offers an alternative nonpetroleum route for the ethylene glycol synthesis.