Selectivity of Ethanol Conversion on Al/Zr/Ce Mixed Oxides: Dehydration and Dehydrogenation Pathways Based on Surface Acidity Properties

Abstract

Zirconia-alumina mixed oxides (Zr + Ce)O 2 À Al 2 O 3 with various mol. ratios (5, 10, 20, 50, and 75 % alumina) were prepared using the sol-gel method. The catalysts were characterised via XRD, SEM, DTA/TG, BET, and FT-IR spectroscopy. The acidities of the catalysts were measured through the absorption of anthraquinone and pyridine probe molecules using EPR and IR spectroscopy, respectively. Catalytic activity and selectivity were investigated for ethanol conversion to acetaldehyde, ethylene, and diethyl ether, which were used as model reactions to identify surface-active sites. The relationship between the surface structure and the dehydration/dehydrogenation activity was evaluated. Diethyl ether formation is promoted by the presence of the ZrO 2 tetragonal phase at a low ZrO 2 /Al 2 O 3 ratio in the sample composition, at which the Lewis acid site has an aluminum-oxygen environment. The reaction mechanism was also discussed. In the low-temperature reaction region, dehydrogenation competes with dehydration; ethylene and acetaldehyde share a common reactive intermediate.

Valorization of (Bio)Ethanol over MoO3/(WO3-ZrO2) Sol-Gel-like Catalysts

“…The selectivity towards ethylene is favoured by reaction temperature due to the endothermic character of the dehydration reaction (DH 298 K = 45 kJ/mol) [8]. For the lowest tested temperature (280 • C), appreciable production of acetic acid was obtained (selectivity of 35.3%), which arises from consecutive oxidation of the formed acetaldehyde which has the same reaction intermediate than ethylene [11]. Increasing reaction temperature, the conversion and the selectivity toward ethylene increase, and the selectivity toward acetic acid decreases.…”

“…Chuklina et al [11] used (Zr+Ce)/Al 2 O 3 mixed-oxide catalysts, prepared by the sol-gel method, to convert ethanol into ethylene, acetaldehyde, and diethyl ether. For low temperatures, the researchers reported a competition between dehydration and dehydrogenation reaction paths because ethylene and acetaldehyde have the same reaction intermediate.…”

Homogeneous vs. heterogeneous catalysts for acceptorless dehydrogenation of biomass-derived glycerol and ethanol towards circular chemistry

“…Chuklina & Zhukova reported zirconia-alumina mixed oxides (Zr + Ce)O 2 + Al 2 O 3 to be active for ethanol dehydrogenation, where the selectivity towards acetaldehyde was highly dependent on the oxide composition. 130 At a low ZrO 2 / Al 2 O 3 ratio, these catalysts promoted the formation of diethyl ether through Lewis acid sites primarily composed of an aluminum-oxygen environment, which facilitated the interaction between an ethoxy group and an activated nondissociated ethanol molecule.…”

EPR characterization of Cu/Al‐Zr‐Ce ethanol dehydrogenation catalysts: Active site development and coking control

“…Our group has designed various approaches to investigate catalyst surface properties by probe‐assisted EPR spectroscopy and superposition spectra analysis in situ mode. [ 28 ] The present study is focused on the characterization of the temperature‐dependent Cu sites formation for Cu‐modified complex oxide samples by EPR spectroscopy. The EPR measurements were performed for the highly efficient in ethanol conversion reaction copper impregnated Al‐Zr‐Ce oxide samples before and after catalysis.…”

“…The EPR measurements were performed for the highly efficient in ethanol conversion reaction copper impregnated Al‐Zr‐Ce oxide samples before and after catalysis. Powders with 5% Al 2 O 3 –[88% ZrO 2 –12% CeO 2 ] (mol %) theoretical oxide composition have various phase composition depending on the calcination temperature (500°C and 950°C for ACZ‐500 and ACZ‐950, respectively), [ 28 ] with 5 wt.% Cu loaded by wet impregnation.…”