Effect of the cerium modification on acid-base properties of Mg-Al hydrotalcite-derived oxide system and catalytic performance in ethanol conversion

The prospects of using cerium as a modifying additive of Mg-Al hydrotalcite-derived oxide system have been estimated by low-temperature nitrogen ad(de)sorption, X-ray diffraction, scanning electron microscopy, H-1 and Al-27 solid-state nuclear magnetic resonance (NMR), X-ray photoelectron and UV-Vis diffuse reflectance spectroscopy techniques. The effect of such tuning of structural-textural characteristics and acid-base properties of the surface on its catalytic performance in ethanol conversion has been studied. Solid-state NMR spectroscopic study of the probe molecule adsorption and temperature-programmed desorption of NH3 and CO2 with mass-spectrometry control are used to determine the nature and strength distribution of acidic and basic sites of Mg-Al(-Ce) oxide systems. It has been found that the selectivity towards 1-butanol up to 68.1% (548 K) is achieved in ethanol conversion over Mg-Al-Ce sample at time-on-stream <= 2 h. At higher time-on-stream, the specific rates of the target product (1-butanol) formation are comparable for both modified and un-modified catalysts, but the products distribution differs. Cerium modification of Mg-Al oxide catalyst leads to increase in specific rate of acetaldehyde formation due to increase in the number of basic sites and their surface density. Wherein, the rate of ethanol dehydration products (ethylene and diethyl ether) is reduced, apparently, due to decrease in a number of Lewis acidic sites formed by Al3+ cations octahedrally coordinated to oxygen.

Automated summary

The study found that cerium-modified Mg-Al oxide systems exhibit higher selectivity towards 1-butanol in ethanol conversion. The modification increases the specific rate of acetaldehyde formation by increasing the number of basic sites and their surface density, while reducing the rate of ethanol dehydration products formation.