Tea catechins as a member of flavan-3-ols subclass with the same skeleton may behave differentially. This study investigated the chemical conversions of 8 catechins under heat treatment with the involvement of epimerization, hydrolysis and oxidation/condensation reactions. Three reactions were enhanced as temperature increased from 30 °C to 90 °C. The epimerization of non-gallated catechins was favored by epi-configuration but hindered by pyrogallol moiety, and the hydrolysis reaction of gallated catechins was facilitated by pyrogallol moiety. Epicatechin and epigallocatechin had the lowest thermostabilities due to epimerization and oxidation/condensation reactions respectively. Sufficient O 2 was not a precondition for the occurrence of chemical conversions of catechins under heat treatment. Non-enzymatic oligomerization occurred to epi type catechins and catechin under heat treatment, and dehydrodicatechins A were mainly responsible for the browning of epicatechin and catechin solutions. The evidence of generation of catechin oligomers provides a novel way to explain sensory change of tea and relevant products during thermal processing.
The high entropy oxides are widely studied as the potential catalytic materials owing to their unique structure and excellent properties. In this work, a new high entropy oxide catalyst MnFeCoNiCuO x was successfully prepared and used for the oxidative condensation reaction of furfural (FUR) and aliphatic alcohol , where the carbon-chain length can be selectively increased under the mild conditions. For the selective oxidative transformation of FUR with n-butanol, a more than 99.0 % conversion of FUR and 91.5 % selectivity of 2-(furanyl-2-methylene) butanal was obtained at 80 ºC for 2 h. In addition, the oxidative condensation of FUR with ethanol, n-propanol, n-pentanol, n-hexanol and n-heptanol was also carried out with the MnFeCoNiCuO x - LiOH as catalyst system in the presence of molecular oxygen , where a moderate to high product yields were acquired. Furthermore, the characterizations of catalyst showed that the existence of abundant oxygen vacancy and high specific area was greatly important to the catalytic reactions .
Xinli Tong,Zhenya Zhang,Yiqi Gao,Yue Zhang,Linhao Yu,Yongdan Li
A novel carbon-chain increasing valorization of furfural (FUR), a cheap bio-based platform compound, has been successfully performed via the catalytic oxidative condensation process with mono-dispersed palladium oxide catalyst. For the reaction of furfural, n-propanol and O 2 , the PdO@TiO 2 exhibited a prominent catalytic activity in which a 77.8% conversion of FUR with 89.2% selectivity of 3-(furan-2-yl)-2-methylacrylaldehyde was obtained. Based on the XRD, SEM, TEM, HRTEM, XPS, and UV–vis results of catalysts, it was concluded that high activity is associated with particle size, uniform distribution of palladium oxide and surface area of the support. Moreover, the recycling experiments confirmed that mono-dispersed palladium oxide catalyst was stable, in which it still kept a good catalytic performance after being recycled for five times. This provided a new route for the selective transformation of the hemicellulose-derived platform compounds.
危险品化学品经营许可证（带存储）