Jinqiu Guo,Zongjing Feng,Jun Xu,Jie Zhu,Guanghui Zhang,Yaping Du,Hongbo Zhang,Chunhua Yan
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)SO4·xH2O catalysts, with 60–70% Ce3+ preserved during the catalysis. High methyl phenols (MPs) selectivity at ∼80% within condensation products was achieved at ∼50% condensation yield (3.0 kPa C2H5OH, 15 kPa H2, Ar balanced, 693 K, 1 atm, gas hourly space velocity (GHSV) ∼5.4 min–1), with acetaldehyde, acetone, 4-heptanone, and 2-pentanone 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 C2H4O 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)SO4 crystal structure was proved to be maintained along with ethanol activation, and the Ce3+–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.
Selective C–H bond oxidation of cyclohexane into KA oil (ketone-alcohol) is of vital importance in both fundamental research and industrial applications while limited by complex reaction network and suffering from low efficiency. In this study, Ce(OH)SO 4 · x H 2 O was chosen as a probe to systematically investigate the C–H bond activation and C–C bond rupture as a function of various reaction parameters, including the reactant/product concentrations, catalyst applied, reaction temperatures, acidic concentrations etc, and found that bi-molecule of C 6 H 12 was probably involved in both C–H bond rupture and C–C bond cleavage and both were controlled by one deprotonation elementary step with ·O 2 – and h + as the key active components, which were supported by parity fittings and primary KIEs determined. In addition, the C–C bond rupture was found to be mainly following C 6 H 10 O to ε-caprolactone and further to linear acids reaction path. Hopefully, this study could help people find/optimize reaction systems in selective hydrocarbon upgradings.
We report here that the reduction degree of the metal at the catalytic interface dominates the reactivity of acetylene hydrogenation, mainly in terms of turnover rates (TORs) and activation energies, which could certainly cause the switch of kinetically relevant steps (KRS) from “C 2 H 3 *+H*” over Ce(OH)SO 4 ·xH 2 O dispersed Pd catalyst to “C 2 H 4 *+H*” elementary step over Pd/CeO 2 . Besides, a compact kinetic model has been established to describe the reaction process and the dissociative mechanism was confirmed by H 2 /D 2 exchange experiment. Meanwhile, the rate-determining step (RDS) and the main adsorbed species of the reaction were confirmed by systematic kinetic studies as well as in-situ FTIR analysis. More importantly, with the aid of parity fitting and gas isothermic adsorption analysis, the energetic relationship among the steps along with the acetylene hydrogenation is quantitatively described, which provides a good support and complement for the previous research, and helps researchers build up advanced reaction systems.
危险品化学品经营许可证（带存储）