We introduce a framework for parameter estimation of microkinetic models via injecting data, collected in optimal regions of the "entire" experimental operating space, in models. We demonstrate this framework by combining differential conversion experimental data without transport limitations and models for ammonia decomposition on Ru/γ-Al 2 O 3 for hydrogen production. Experiments indicate that there is significant H 2 inhibition even at low ammonia conversions. Statistical model discrimination techniques indicate that multiple microkinetic parameter sets are able to describe quantitatively the experimental data, and some global rate expressions are also adequate. Among the best microkinetic models, nitrogen adsorption/desorption and the NH x dehydrogenation reactions are the kinetically significant reactions. It is found that macroscopic data (conversion) are insufficient for complete model discrimination; microscopic scale data are proposed for further model discrimination.
The Schiff base (Hfsal-dmen) derived from 3-formylsalicylic acid and N,N-dimethyl ethylenediamine has been covalently bonded to chloromethylated polystyrene to give the polymer-bound ligand, PS-Hfsal-dmen (I). Treatment of PS-Hfsal-dmen with [V(IV)O(acac)(2)] in the presence of MeOH gave the oxidovanadium(IV) complex PS-[V(IV)O(fsal-dmen)(MeO)] (1). On aerial oxidation in methanol, complex 1 was oxidized to PS-[V(V)O(2)(fsal-dmen)] (2). The corresponding neat complexes, [V(IV)O(sal-dmen)(acac)] (3) and [V(V)O(2)(sal-dmen)] (4) were similarly prepared. All these complexes are characterized by various spectroscopic techniques (IR, electronic, NMR, and electron paramagnetic resonance (EPR)) and thermal as well as field-emission scanning electron micrographs (FE-SEM) studies, and the molecular structures of 3 and 4 were determined by single crystal X-ray diffraction. The EPR spectrum of the polymer supported V(IV)O-complex 1 is characteristic of magnetically diluted V(IV)O-complexes, the resolved EPR pattern indicating that the V(IV)O-centers are well dispersed in the polymer matrix. A good (51)V NMR spectrum could also be measured with 4 suspended in dimethyl sulfoxide (DMSO), the chemical shift (-503 ppm) being compatible with a VO(2)(+)-center and a N,O binding set. The catalytic oxidative desulfurization of organosulfur compounds thiophene, dibenzothiophene, benzothiophene, and 2-methyl thiophene (model of fuel diesel) was carried out using complexes 1 and 2. The sulfur in model organosulfur compounds oxidizes to the corresponding sulfone in the presence of H(2)O(2). The systems 1 and 2 do not loose efficiency for sulfoxidation at least up to the third cycle of reaction, this indicating that they preserve their integrity under the conditions used. Plausible intermediates involved in these catalytic processes are established by UV-vis, EPR, (51)V NMR, and density functional theory (DFT) studies, and an outline of the mechanism is proposed. The (51)V NMR spectra recorded for solutions in methanol confirm that complex 4, on treatment with H(2)O(2), is able to generate peroxo-vanadium(V) complexes, including quite stable protonated peroxo-V(V)-complexes [V(V)O(O)(2)(sal-dmen-NH(+))]. The (51)V NMR and DFT data indicate that formation of the intermediate hydroxido-peroxo-V(V)-complex [V(V)(OH)(O(2))(sal-dmen)](+) does not occur, but instead protonated [V(V)O(O)(2)(sal-dmen-NH(+))] complexes form and are relevant for catalytic action.
The Schiff base (Hfsal-aepy) derived from 3-formylsalicylic acid and 2-(2-aminoethyl)pyridine has been covalently bonded to chloromethylated polystyrene cross-linked with 5% divinylbenzene (PS-Hfsal-aepy). Treatment of [V(IV)O(acac)(2)] with PS-Hfsal-aepy in dimethylformamide (DMF) gave the oxidovanadium(IV) complex PS-[V(IV)O(fsal-aepy)(acac)] 1, which on oxidation yielded the dioxidovanadium(V) PS-[V(V)O(2)(fsal-aepy)] 2 complex. The corresponding neat complexes, [V(IV)O(sal-aepy)(acac)] 3 and [V(V)O(2)(sal-aepy)] 4 have also been prepared. The compounds are characterized in solid state and in solution, namely by spectroscopic techniques (IR, UV-Vis, EPR, (1)H, (13)C and (51)V NMR), thermal as well as field-emission scanning electron micrograph (FE-SEM) studies. The crystal and molecular structure of [V(IV)O(sal-aepy)(acac)] was solved by single-crystal X-ray diffraction. It is a monomeric complex with the tridentate sal-aepy ligand bound equatorially and the two O-atoms of acac(-) bound at equatorial and axial positions. These complexes catalyze the hydroamination of styrene and vinyl pyridine with amines (aniline and diethylamine) yielding a mixture of two hydroaminated products in good yield. Amongst the two hydroaminated products, the anti-Markovnikov product is favored over the Markovnikov one. Plausible intermediates involved in these catalytic processes are established by UV-Vis, EPR and (51)V NMR studies, and an outline of the mechanism is proposed. The EPR spectrum of the polymer supported V(IV)O-complex 1 is characteristic of a magnetically diluted V(IV)O-complex, the resolved EPR pattern indicating that the oxidovanadium(IV) centers are well dispersed in the polymer matrix. Neat complexes exhibit lower conversion along with lower turnover frequency as compared to their polymer-anchored analogues. The polymer-anchored heterogeneous catalysts are free from leaching during catalytic action and are recyclable.
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