Gases qualitative interpretation

The authors provided only a qualitative interpretation of their results. They proposed that the better performance of the monolith relied on the beneficial effects of concentration and temperature boundary layers. The expected effect of interphase mass transfer limitations was, in fact, a decrease of O2 concentration at the gas—catalyst interface, with better control of the vanadium valence state and consequently a partial suppression of consecutive oxidation reactions (due to a more important kinetic dependence of deep oxidations on O2 concentration than the desired selective oxidation). The presence of heat transfer limitations was then believed to establish a catalyst temperature higher than the gas-phase temperature, thus promoting heterogeneously-initiated homogeneous reactions at the gas-catalyst interface, with production of peroxo radical species and eventually propylene. ... 

The real interaction of chemisorbed molecules, however, can be rather complicated [82,93]. In particular, the parameters of the interaction between neighbouring molecules can change with varying surface coverages due to the collective interaction of adsorbed molecules with solid surfaces. Therefore the lattice gas model that utilizes a small number of parameters cannot describe, even qualitatively, the entirety of surface processes. Nevertheless, this model can be applied to interpret some individual regularities,... 

Quantitative and qualitative changes in chemisorption of the reactants in methanol synthesis occur as a consequence of the chemical and physical interactions of the components of the copper-zinc oxide binary catalysts. Parris and Klier (43) have found that irreversible chemisorption of carbon monoxide is induced in the copper-zinc oxide catalysts, while pure copper chemisorbs CO only reversibly and pure zinc oxide does not chemisorb this gas at all at ambient temperature. The CO chemisorption isotherms are shown in Fig. 12, and the variations of total CO adsorption at saturation and its irreversible portion with the Cu/ZnO ratio are displayed in Fig. 13. The irreversible portion was defined as one which could not be removed by 10 min pumping at 10"6 Torr at room temperature. The weakly adsorbed CO, given by the difference between the total and irreversible CO adsorption, correlated linearly with the amount of irreversibly chemisorbed oxygen, as demonstrated in Fig. 14. The most straightforward interpretation of this correlation is that both irreversible oxygen and reversible CO adsorb on the copper metal surface. The stoichiometry is approximately C0 0 = 1 2, a ratio obtained for pure copper, over the whole compositional range of the... 

Gas/crystal comparisons are as of yet mainly confined to registering structural differences. The interpretation of these results is at a qualitative initial stage. Further investigation of such differences will enhance our understanding of the intermolecular interactions in crystals. 

Gas chromatography coupled to mass spectrometry is a widely used analytical method [31] but does require prior reduction of the involatile N-oxides. Additionally, there are problems associated with some alkaloids that require prederivatization to enhance the GC characteristics. These requirements for prederivatization can adversely affect the GG-MS interpretation, especially at trace levels of alkaloids [32]. Gombined SPE-LC-MS approaches have provided methods for qualitative profiling and quantitative analysis of pyrrolizidine alkaloids and their N-oxides. 

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