Combined kinetics of catalytic and non-catalytic reactions in the oxidative coupling of CH4. (8p.)

The heterogeneously catalyzed oxidative CH4 coupling reaction is known to proceed in a complex mechanism consisting of surface- and homogeneous gas phase reactions. The presented paper deals with the mathematical simulation of this reaction using a complex reaction model that combines a homogeneous gas phase model consisting of more than 180 reactions and a set of heterogeneous surface reactions for an Eley-Rideal mechanism. By fitting the simulation results to experimental data for a PbO/ - Al2O3 catalyst kinetic parameters for the catalytic elementary reactions were obtained. Sensitivity analyses were performed to show the importance of the individual catalytic reaction steps.

The partial oxidation of propane under mild aqueous conditions with H2O2 and ZSM-5 catalysts

We report the oxidation of propane under mild aqueous conditions using H2O2 as the oxidant. Various reaction conditions have been studied with a view to optimising the conversion of propane in the presence of a Fe/ZSM-5 (30) catalyst. Process optimisation afforded 52% propane conversion in 0.5 h at a temperature of 70 \ub0C. C3 products are shown to undergo sequential catalytic C-C scission and oxidation reactions in the presence of the catalysts, yielding C2 and C1 products. This leads to an inverse relationship between propane conversion and reaction selectivity. Addition of Cu to Fe/ZSM-5 (30) shifted reaction selectivity towards propene ( 6434%) with increasing conversion

The Low-Temperature Oxidation of Propane by using H2O2 and Fe/ZSM-5 Catalysts: Insights into the Active Site and Enhancement of Catalytic Turnover Frequencies

Fe-containing ZSM-5 catalysts are reported to be efficient catalysts for the partial oxidation of propane to oxygenated products at reaction temperatures as low as 50 \ub0C in an aqueous phase reaction when using the green oxidant H2O2. It was previously proposed that extra framework Fe species at the exchange sites of the zeolite are responsible for activation of both the alkane and hydrogen peroxide. Through a systematic study of the influence of framework topology and exchange properties, it is now shown that this high catalytic activity is specific to the MFI-type Br\uf8nsted acidic zeolite ZSM-5. Furthermore, through a simple aqueous acid washing treatment, leaching of approximately 77 % of iron present within a Fe/ZSM-5 catalyst only caused the relative propane conversion to decrease by 17 %; implying that most of the initially loaded Fe does not actually contribute to the catalytic activity. This small change in conversion after \u2018excess\u2019 Fe removal, amounts to a three-fold increase in turnover frequency (TOF) (Fe) from 66 h 121 to 232 h 121 compared with the parent Fe/ZSM-5 catalyst. By comparing these samples, it is shown by NH3 temperature-programmed desorption, 27Al magic angle spinning NMR spectroscopy, X-ray photoelectron spectroscopy and TEM analysis that surface iron oxide species are effectively spectators in the oxidation of propane with H2O2. This provides further insight as to the location and true nature of the catalytically active Fe species