Back Cover: Direct Catalytic Conversion of Ethanol to C<sub>5+</sub> Ketones: Role of Pd–Zn Alloy on Catalytic Activity and Stability (Angew. Chem. Int. Ed. 34/2020)

Subramaniam, Senthil; Guo, Mond F.; Bathena, Tanmayi; Gray, Michel J.; Zhang, Xiao; Martinez, Abraham; Kovařík, Libor; Goulas, Konstantinos A.; Ramasamy, Karthikeyan

doi:10.1002/anie.202008185

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“…MPs might be obtained from C 5+ ketone cyclization, which would be effectively generated from ethanol following a series of C–C bond coupling steps. − That is clearly environmentally benign and promising. For example, Ramasamy et al directly prepared C 5+ ketone (with 2-pentanone (2-PNO) and 4-heptanone (4-HPO) as the main components) from ethanol over 0.1% Pd-ZnO-ZrO 2 at 643 K, 2 MPa, with acetone as the key reaction intermediate. Small amounts of MPs were determined from their system, which indicates that the selective generation of MPs from ethanol is possible.…”

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confidence: 99%

Facile Preparation of Methyl Phenols from Ethanol over Lamellar Ce(OH)SO₄·xH₂O

Guo

Feng

et al. 2021

ACS Catal.

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Ethanol transformation with high product selectivity is a great challenge, especially for high weight molecules. Here, we show a combination study of kinetic, thermodynamic, and in situ spectroscopy measurements to probe the selective upgrading of ethanol over lamellar Ce(OH)SO 4 •xH 2 O catalysts, with 60− 70% Ce 3+ preserved during the catalysis. High methyl phenols (MPs) selectivity at ∼80% within condensation products was achieved at ∼50% condensation yield (3.0 kPa C 2 H 5 OH, 15 kPa H 2 , Ar balanced, 693 K, 1 atm, gas hourly space velocity (GHSV) ∼5.4 min −1 ), with acetaldehyde, acetone, 4-heptanone, and 2pentanone as the key reaction intermediates. Kinetic measurements with the assistance of isotope labeling proved that MPs generated from the kinetically relevant step (KRS) of C−C bond coupling of enolate nucleophilically attacks surface C 2 H 4 O following a Langmuir−Hinshelwood model. Low ethanol and water pressures and high acetaldehyde and hydrogen pressures were proved to be favored for MPs generation rather than dehydration, in which hydrogen could reduce the amount of lattice oxygen and facilitate the preparation of MPs while water and ethanol both compete with acetaldehyde for active sites during catalysis. On the basis of in situ X-ray diffraction (XRD), quasi-in situ X-ray photoelectron spectroscopy (XPS), and Raman characterizations, the Ce(OH)SO 4 crystal structure was proved to be maintained along with ethanol activation, and the Ce 3+ −OH Lewis acid−base pair was proved to be the active species for the selective C−C bond coupling. The KRS assumption was also supported by the apparent activation energy assessment within the reaction network on dehydration, dehydrogenation, aldol condensation, and cyclization and a series of negligible kinetic isotope effects (KIEs). This system can be easily extended to some other systems related to C−C bond coupling and is attracting attention on converting oxygenate platform molecules over lanthanide species.

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