Effect of Catalyst Structure and Acid–Base Property on the Multiproduct Upgrade of Ethanol and Acetaldehyde to C4 (Butadiene and Butanol) over the Y–SiO2 Catalysts

The multiproduct upgrade of ethanol and acetaldehyde to butadiene as a high-value chemical and butanol as a biofuel was investigated over the Y–SiO2 heterogeneous catalysts. The sum selectivity of butanol and butadiene is over 90% for the Y–SiO2 catalysts with Y/Si ratios from 0.05 to 0.35, while the distribution changes with the Y/Si ratio. The highest butadiene selectivity of 81.2% with a butanol selectivity of 10.3% was obtained over the Y–SiO2 catalyst with a Y/Si ratio of 0.05. To study the effect of the catalyst structure and acid–base property on catalytic performance, the Y–SiO2 catalysts with different Y/Si ratios were further comprehensively characterized by techniques including nitrogen adsorption–desorption, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), 29Si cross–polarization/magic-angle spinning nuclear magnetic resonance (29Si CP MAS NMR), Fourier transform infrared resonance (FTIR), UV–Vis diffuse reflectance spectra (UV–Vis DRS), temperature-programmed desorption of NH3 and CO2 and NH3 (NH3-TPD and CO2-TPD), and FTIR spectroscopy of adsorbed pyridine (Pyridine-IR). Results from XPS, 29Si CP MAS NMR, FTIR, and UV–Vis DRS reveal the electron transfer and the formation of chemical linkages between Y2O3 and SiO2 rather than the simple deposition of Y2O3 on the surface of the fumed silica. What is more, the amounts and coordination of Y–O–Si linkages on the surface of the fumed silica vary with the Y/Si ratio varying, thus resulting in variation of the acid–base property. Combining with the catalytic activity, NH3-TPD, CO2-TPD, and Pyridine-IR results indicate that the strength of acid and base sites has a significant role on the catalytic performance. The base sites with stronger strength contribute to the formation of butanol. To obtain a high butadiene selectivity, a balance of the acid–base property is necessary. A combination of Y3+ Lewis acid sites with a higher density ratio of stronger acid sites to the total acid sites and base sites with an intermediate strength is inclined toward a high butadiene selectivity. It means that a proper distribution between butadiene and butanol could be achieved by tuning the acid–base property of theY–SiO2 catalysts on the premise of a high C4 selectivity of over 90%.