Upgrade of Solvent-Free Acetone–Butanol–Ethanol Mixture to High-Value Biofuels over Ni-Containing MgO–SiO2 Catalysts with Greatly Improved Water-Resistance

The upgrade of acetone–butanol–ethanol (ABE) mixture from biomass to high-value biofuels has aroused increasing attention. However, a reported heterogeneous catalyst, metal-containing MgAl-hydrotalcite (HT), is confronted with a serious water-resistance problem due to an inherent memory effect of HT materials. With the aim of exploring catalysts with improved water-resistance, metal-containing MgO–SiO2 catalysts were synthesized and evaluated. An investigation on the effect of metal type including Ni, Cu, Fe, Zn, and Co, metal loading, and reaction temperature on catalytic performance indicates that the 10 wt % Ni–MgO–SiO2 catalyst provides the best catalytic performance, giving a yield of 81.5% to C5–C15 ketones and alcohols at 240 °C. As expected, the catalyst exhibits an excellent water-resistance. It could tolerate up to 3 wt % water, which was much higher than 0.5 wt % over that of Cu- or Pd-HT as reported. Results from XRD and 29Si MAS NMR analyses indicate that the high water-resistance could be ascribed to the more stable structure of magnesium silicates formed in the catalyst than HT materials. For a further study of the effect of catalyst property on catalytic performance, 10 wt % Ni–SiO2, 10 wt % Ni–MgO, and 10 wt % Ni–MgO–SiO2 catalysts were investigated and characterized. Results from CO2-TPD, pyridine-IR, and NH3-TPD analyses reveal that the catalytic performance is significantly affected by an acid–base property. Obtaining a high catalytic performance necessitates a cooperation of enough acidic sites and basic sites.