Effects of surface hydroxyl groups induced by the co-precipitation temperature on the catalytic performance of direct synthesis of isobutanol from syngas

A series of Zn-Cr oxides catalysts with different content of surface hydroxyl groups were prepared at different co-precipitation temperature. These catalysts were used for direct synthesis of isobutanol from syngas with an aim to investigate the effect of co-precipitation temperature on the catalytic activity of Zn-Cr catalysts. The co-precipitation temperature had a strong influence on surface OH groups leading to the different activities of ZnCr catalysts. Catalysts characterizations by XPS, XRD, H₂-TPR, CO₂-TPD, in situ FTIR of CO absorption and DFT calculation clearly revealed that the surface OH groups played important role in the adsorption and activation of CO. The adsorption energy of CO is intensified by the presence of surface OH, and it is easier to form formats than carbonates owning to the low activation barrier and reaction energy. Therefore, selectivity for alcohols showed an increased tendency with increasing the surface OH content on catalysts. Among all ZnCr catalysts, catalyst prepared at 60 °C (ZC-60) showed the best catalytic performance due to the highest concentration of surface OH groups.