The oxidative coupling of methane (OCM) to C 2 -hydrocarbons (C 2 H 4 and C 2 H 6 ) is attractive both from fundamental (selective C−H bond activation) and applied viewpoints. The main drawback hindering its commercialization is the low selectivity to C 2 -hydrocarbons due to their further oxidation to carbon oxides. In this respect, we focused on elucidating fundamentals of the previously reported positive effect of water on the activity and selectivity in the OCM reaction over MnO x -Na 2 WO 4 /SiO 2 by means of steady-state kinetic and mechanistic tests at ambient pressure as well as temporal analysis of products with sub-millisecond resolution and isotopic tracers in vacuum. The obtained results cannot be rationalized by the earlier developed concepts explaining the role of water in the OCM reaction over this catalyst system. In addition, the selectivity-enhancing water effect was determined for MnO x

The understanding of the reaction mechanism of product formation in the oxidative coupling of methane (OCM) is the prerequisite for designing catalysts with improved selectivity to the desired products, i.e., C 2 H 6 and C 2 H 4 (C 2 hydrocarbons). One step in this direction is to understand the kind of oxygen species involved in the selective and nonselective reactions. Against this background, a series of kinetic and mechanistic tests of the OCM reaction with N 2 O (N 2 O−OCM) were carried out over the Mn−Na 2 WO 4 /SiO 2 system in the absence and the presence of cofed water. The usage of N 2 O instead of O 2 was proven to suppress the direct oxidation of CH 4 to CO 2 in favor of the formation of C 2 hydrocarbons. This inhibition was explained by a lower concentration of surface biatomic oxygen species participating in the formation of CO 2 . The formation of such species from O 2 was supported by oxygen isotopic exchange and electron paramagnetic resonance (EPR) tests. As proven by in situ UV−vis tests under various reaction conditions at 750 °C, N 2 O−OCM and O 2 −OCM mainly proceed through a Mars van Krevelen sequence. As MnO x is reduced faster than Na 2 WO 4 , it should be primarily involved in oxidant activation. In comparison with O 2 , N 2 O was proven to reoxidize reduced catalysts significantly slower. This results in reducing surface density (spatial separation) of lattice oxygen species in N 2 O−OCM that is unfavorable for the undesired oxidation reactions leading to carbon oxides. As a result, the selectivity to C 2 hydrocarbons increases. This knowledge is essential for catalyst design through controlling the rates of generation and consumption of oxygen species. A further aspect of this work is the positive effect of H 2 O on the rate of methane conversion and the selectivity to C 2 hydrocarbons in N 2 O−OCM. The strength of this effect on the activity is lower than in O 2 −OCM. The enhancing effect was related to H 2 O-mediated transformation of surface biatomic oxygen species into monatomic ones.

Until now a great number of various materials have been tested for the oxidative coupling of methane (OCM). On the basis of previous statistical analysis of OCM-related literature data, we...

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In this study, we investigated gene delivery properties of Jeffamine-cored polyamidoamine (PAMAM) dendrimers (JCPDs). The effects of dendrimer concentration, generation, and core size on the gene delivery have been analyzed. The experimental results showed that the JCPD effectively delivered plasmid DNA inside the HeLa cells, and the transfection efficiency improved considerably as the number of generation increased. The cytotoxicity of JCPD in different concentration was tested for HeLa cell line. JCPD was complexed with a lacZ gene carrying plasmid and tested for transfection efficiency using quantitative β-galactosidase expression assay. Additionally, confocal microscopy results revealed that JCPD effectively delivered green fluorescent protein-expressing plasmid into HeLa cells and produced fluorescent signal with satisfactory efficiency. The highest transfection efficiency was obtained from JCPDs G4 and G5, which mixed with expression plasmid vectors at a 10/1 weight ratio. These results indicated that under optimized conditions, JCPD can be considered as an efficient transfection reagent and can be effectively used for gene delivery applications.