Direct Synthesis of Isobutanol from Syngas over Nanosized Cu/ZnO/Al₂O₃ Catalysts Derived from Hydrotalcite-like Materials Supported on Carbon Fibers

The Cu/ZnO/Al 2 O 3 catalyst can be utilized to directly synthesize isobutanol from syngas at low temperatures, and carbon fibers (CFs) are widely used as catalyst supporter. However, little is known about the effect of CFs on Cu/ZnO/Al 2 O 3 catalysts. In this work, we report the effects of CFs on catalysis and structure of Cu/ZnO/Al 2 O 3 catalysts. The composites containing Cu/ZnO/Al 2 O 3 nanoparticles and various contents of CFs were successfully prepared by a coprecipitation method. The catalytic performances of Cu/ZnO/Al 2 O 3 catalyst and the composites were evaluated. Compared with Cu/ZnO/Al 2 O 3 catalyst without CFs, the composites show higher CO conversion and selectivity for isobutanol. Addition of 30% CFs is optimal for synthesis of isobutanol. All the samples were characterized by BET, XRD, H 2 –TPR, SEM–EDS, CO–TPD, and EIS to further disclose the reason for better catalytic performance of the composites. We found that CFs promote dispersion of Cu/ZnO/Al 2 O 3 nanoparticles and thus result in an increase in specific surface area and exposure of more easily accessible Cu 2+ cations, which promotes conversion of CO. The increase in isobutanol selectivity results from the increase in CO conversion, improvement of electron-transferring property, and enhancement of nondissociative CO adsorption. However, addition of overabundant CFs leads to incomplete cover of Cu/ZnO/Al 2 O 3 nanoflakes due to the substantial decrease in content of the Cu/ZnO/Al 2 O 3 phase, which causes a decrease in CO conversion and selectivity for isobutanol.