Full use of factors promoting catalytic performance of chitosan supported manganese porphyrin.

In order to make full use of the impact of internal and external factors on the performance of title catalyst for ethyl benzene oxidation, the key internal influencing factors on the catalytic performance were modulated by coordinating and grafting manganese porphyrin to mesoporous and macroporous chitosan, and the important external factors (i.e. oxidation reaction conditions) were optimized using Response Surface Methodology. Under the Response Surface Methodology optimized oxidation reaction conditions (176.56 °C, 0.59 MPa, and 0.25 mg amount of manganese porphyrin), the catalyst could be used at least five times. The ethyl benzene conversion, catalyst turnover numbers, and yields reached up to 51.2%, 4.37 × 106 and 36.4% in average, respectively. Compared with the other optimized oxidation reaction conditions, the corresponding values increased 17%, 26% and 53%. Relative to the manganese porphyrin, the catalytic performance and efficiency of the immobilized catalyst had notably increased.

Highly Active Catalysis of Cobalt Tetrakis(pentafluorophenyl)porphyrin Promoted by Chitosan for Cyclohexane Oxidation in Response-Surface-Methodology-Optimized Reaction Conditions.

We aimed at elevating catalytic performances of cobalt tetrakis(pentafluorophenyl)porphyrin (Co TPFPP) through axial coordination, nanocavities, and covalently grafting action. The Co TPFPP was immobilized onto nanoporous and nonporous chitosan, forming Co TPFPP/np- and nonp-CTS catalysts, respectively. The catalysts were characterized by various spectroscopic techniques. The catalytic performances of these catalysts for cyclohexane oxidation under response-surface-methodology-optimized oxidation reaction conditions were estimated and compared. Co TPFPP/np-CTS was an excellent catalyst at aspect of catalytic activity, exhibiting the considerable potential reusability, 24.2 mol % yields (KA oil : cyclohexanone and cyclohexanol) in average, and total turnover frequencies (TOFs) of 3.25×106 h-1. This is attributed to the structural characteristics of the Co TPFPP/np-CTS catalyst: the cobalt porphyrin molecules could be highly scattered on CTS, forming the independent active sites, and were not leached. The axial coordination exerted the most important effect on the catalytic activity, and the covalent grafting action had a decisive effect on the increase of the total TOFs and on the reusability of the catalyst.

A theoretical study on reductive debromination of polybrominated diphenyl ethers.

Recent progress has been made in the reductive debromination of polybrominated diphenyl ethers (PBDEs) by nanoscale zero-valent iron (nZVI). To better understand the mechanism of this reaction, seven selected BDE congeners and their anions were investigated at the density functional theory (DFT) level using four different methods, including B3LYP/6-31G(d), B3LYP/6-31+G(d), B3LYP/6-31G(d,p) and B3LYP/6-311G(d,p). The cleaved C-Br bonds observed in the equilibrium structures of anionic PBDEs were adopted as the probe of the susceptible debromination position of PBDEs in the presence of nZVI, and the proposed major reaction pathways based on our calculations can satisfactorily conform to the reported experimental results. The debromination preference is theoretically evaluated as meta-Br > ortho-Br > para-Br. In addition, both the calculated frontier orbital energies and adiabatic electronic affinities were found to be highly related to their experimental reductive debromination rate constants. The highest linear regression coefficient was observed in the case using the energy of lowest unoccupied molecular orbital as the molecular descriptor obtained from B3LYP/6-31G(d) (R(2) = 0.961, n = 7) or B3LYP/6-31G(d,p) (R(2) = 0.961, n = 7). The results clearly showed the evidence of an electron transfer mechanism associated with this reductive debromination reaction.

[Determination of trace lead in Chinese medicinal materials by GFAAS with PdCl2 as a matrix modifier].

A method for the determination of lead in Chinese medicinal materials by GFAAS with PdCl2 as a matrix modifier was established. By comparing PdCl2 with NH4H2PO4 in improving effect on the determination of Pb, the dosage of PdCl2, acidity of medium, interference of coexistent ion, recovery of the method, precision of the method, and the detection limit were checked. The programmed temperature of graphite furnace was optimized. The results show that the improving effect of PdCl2 on Pb determination is better than that of NH4H2PO4. The dosage of PdCl2 is 0.3 microg. The best medium should be 1.0% HCl. The three kinds of acids, 0.4% H2SO4, 1.0% HClO4 and 1.8% HCl, did not weaken the signal of lead. The recovery of the method is 90%-104% and the precision is < 5.0%. The characteristic mass is 8.5 pg. The detection limit is 0.066 mg x kg(-1). It is concluded that the method is simple, sensitive, accurate and credible, and can be used widely.