Anna Zheng

Bio: Anna Zheng is an academic researcher from East China University of Science and Technology. The author has contributed to research in topics: Catalysis & Allylic rearrangement. The author has an hindex of 2, co-authored 5 publications receiving 7 citations.

Role of Organic Fluoride Salts in Stabilizing Niobium Oxo-Clusters Catalyzing Epoxidation.

Abstract: We present here that easily available organic salts can stabilize/modify niobium (Nb) oxo-clusters. The as-synthesized Nb oxo-clusters have been characterized by various methods. These Nb oxo-clusters were catalytically active for the epoxidation of allylic alcohols and olefins with H2O2 as an oxidant. Notably, Nb-OC@TBAF-0.5 appeared as highly dispersed nanosized particles and showed the highest catalytic activity, which can be attributed to the following reasons on the basis of characterization. First, the strong coordination of fluorine ions with Nb sites and the steric protection with bulky organic cations led to high stabilization and dispersion of the oxo-clusters in the course of the reaction. Second, a hydrogen-bond interaction between the coordinated fluorine atom and the -OH group of allylic alcohol favored the epoxidation reaction. Third, the electron density of Nb sites decreased due to the strong electron-withdrawing ability of F- adjacent to Nb sites, thus promoting the electrophilic oxygen transfer to the C═C bond.

Reduced Amino Acid Schiff Base-Iron(III) Complexes Catalyzing Oxidation of Cyclohexane with Hydrogen Peroxide

Abstract: Reduced amino acid Schiff base‐iron(III) complexes have been developed and employed as catalysts for the selective oxidation of cycloalkanes and aromatics into alcohols/ketones and phenols with H2O2 as an oxidant, respectively. The iron complexes catalyze the oxidation reaction via a heterogeneous manner and are capable to be recyclable.

Water-soluble niobium peroxo-complexes as precursors for the preparation of Nb-based oxide catalysts (poster)

Abstract: In the frame of research aimed at developing new synthetic procedures of multimetallic Nb-based catalysts, peroxo complexes of niobium(V) of general formula A I 3 [Nb(O 2 ) 4 ] and A I 3 [Nb(O 2 ) x (H y L)]. n H 2 O (A I : NH 4 +, CN 3 H 6 + (gu); L: oxalate, tartrate, citrate) have been prepared and characterized on the basis of elemental and thermal analysis, FTIR and 13 C-NMR spectra. The crystal structure of (gu) 3 [Nb(O 2 ) 4 ] and (gu) 3 [Nb(O 2 ) 2 (C 2 O 4 ) 2 ].2H 2 O have been determined. The application of the obtained Nb complexes as precursors for the preparation of silica-supported Nb-Mo-O catalysts has been demonstrated. Combining Nb peroxo-carboxylato compounds with analogous Mo(VI) compounds in a silica-impregnation method carried out in aqueous medium leads to the formation of the supported Nb 2 Mo 3 O 14 phase.

Molecular, supramolecular and solution structures ofperoxovanadium complexes with ON and O3N donor set ligands: twonew types of cationic-anionic peroxovanadium(V)peroxovanadates(V)

Abstract: The complexes, [VO(O-2)(pa)(2)] ClO4 . 3H(2)O ( 1), [VO(O-2)(pa)(2)][ VO(O-2)(2)(pa)] . 3H(2)O (2), [VO(O-2)(pa)(2)][VO(O-2)( ada)] . 2H(2)O ( 3) and [VO(O-2)(pa)(pca)] . H2O ( 4) [pa = picolinamide, ada = carbamoylmethyliminodiacetate( 2-) and pca = 2- pyrazinecarboxylate(1-)], were synthesized. 2 and 3 are new types of peroxovanadium complexes: monoperoxovanadium diperoxovanadate ( 2) and monoperoxovanadium monoperoxovanadate ( 3). The complexes were characterized by chemical analysis and IR spectroscopy, and 1, 3 and 4 also by X-ray analysis. The structure of 1 is disordered, with alternating positions of the oxo and peroxo ligands. The peroxo oxygen atoms, O-p, in 1 are involved in weak hydrogen bonds with water molecules and close intramolecular C - H...O-p bonds [d(H...O-p) similar to 2.0 Angstrom]. The supramolecular structure of 1 is formed by a network of hydrogen bonds and strong attractive intermolecular pi - pi interactions between the pyridine rings. The supramolecular architecture in 4 is constructed by (N, O) - H...O hydrogen bonds between the neutral complex molecules and water of crystallization. The peroxo oxygen atoms in 4 form intramolecular C - H...O-p bonds [d( H...O-p) = 2.303 Angstrom]. The pa and pca ligands are ON coordinated via the oxygen atoms of the C(NH2)=O and COO- groups, respectively, and nitrogen atoms of the heterocyclic rings, and ada as a tetradentate O3N ligand. The thermal analysis of 4 showed that the loss of water of crystallization and the active oxygen release (T-min/degreesC 82, T-max/degreesC 165) are, under given conditions, individual processes separated by the temperature interval 90 - 132 degreesC. The solution structures and stability were studied by UV-VIS and V-51 NMR spectroscopies.

Phase-dependent photocatalytic selective oxidation of cyclohexane over copper vanadates

Abstract: In this work, copper vanadates with different crystal phases were prepared via a simple sol-gel method, and used as photocatalysts for selective oxidation of cyclohexane to cyclohexanol and cyclohexanone (KA-oil)....