Fast synthesis of MgO–Al2O3 systems: effect on physicochemical characteristics and catalytic properties in Guerbet condensation of ethanol

A series of hydrotalcite-derived Mg–Al oxide systems with Mg/Al atomic ratios of 2 and 3 were synthesized. The hydrotalcite of Mg–Al-2 and Mg–Al-3 samples was prepared for 24 h, and Mg–Al-2-Fast and Mg–Al-3-Fast samples were kept only for 1 h. The physicochemical characteristics of the samples were studied by X-ray diffraction, scanning electron microscopy, and 27Al nuclear magnetic resonance. The surface area of the samples was determined by low-temperature N2 ad(de)sorption at 77 K. NH3 and CO2 temperature-programmed desorption was applied to determine the acid and base sites of the surface. Based on the study of Mg–Al oxide samples with different times of hydrotalcite preparation, it was found that reducing the maturation time of the mother liquor after coprecipitation from 24 to 1 h increased the volume and the surface area of mesopores and external specific area of the samples, and also the concentration of weak and medium weak base sites. These in turn increase the activity of the catalysts and the selectivity of 1-butanol formation in the process of Guerbet condensation of ethanol. The highest 1-butanol selectivity of 64% and the yield of 23.4% are achieved over the Mg–Al-2-Fast catalyst at 548 K (with stable selectivity of 64% up to 12 h).