Modelling of TPR

The modelling of TPR patterns has not received much attention. Nevertheless, the results depend on the experimental conditions and modelling will be necessary when the results of different authors have to be compared. Moreover, the kinetic and thermodynamic data obtained are very useful. 

Carbonaceous deposits, formed during the hydrogenation of ethylene (150-450 C) over the cobalt foil model catalyst, were investigated by TPO, TPR and SEM methods. The cataljdic tests performed under the transient conditions provided the information on the mechanism of ethylene hydrogenation. The quantitative results of the deposit oxidation were related to the number of metallic active centers measured by TPO and TPR. The reaction temperature was found to exert the most profound impact on both the deposit forms and the deposit functions in the catalytic reaction. Below 300 C only a fraction of the deposit was found to block the metallic active centers and the other part appeared non-reactive in the hydrogenation. Above 400 C the regeneration of the catalyst activity was associated with the difiusion of cobalt atoms to a deposit surface. The results were confronted with the model of deactivation postulated before for CO2 hydrogenation [1]. 

The aim of this study was to develop a new experimental basis for testing the model of deactivation caused by the inactive carbonaceous deposit. Deactivation of the model cobalt foil catalyst was studied in the hydrogenation of ethylene. The focus was on the conditions of ethylene hydrogenation under which the deposits might occur as well as on the determination of their forms and functions in the reaction network. To do this temperature-programmed reactions (TPR and TPO) and microscopic methods (SEM) were applied in conjunction with catalytic tests and stop-flow transient kinetic experiments. 

Liebske et al. [6] were among the first to propose a model of the various phases that could be present as a function of pretreatment conditions in a Pt/AUOs catalyst prepared from Cl precursors. These phases, however, were not correlated with the catalyst s activity. Based on temperature-programmed reduction (TPR) of Pt catalysts oxidized at different temperatures, Hwang and Yeh [7] concluded that four types of oxide species could be... 

The authors have made detailed investigations of the effect of coexisting gas on reaction (2.2) and found that the presence of H2O (water vapor) and small concentrations of SO2 substantially promote this reaction. Figure 2.8 shows the results of TPR of a carbon black (model soot) in loose contact with Pt/Si02 under different... 

The characteristics of this kinetic superposition are strongly dependent on experimental parameters and will be different for both fixed bed reactors and the microbalance configuration. Any further interpretation of the data of Fig. 2.12 is therefore omitted. It is known, however, that under all circumstances the activation process will be controlled by a complicated interaction of kinetic influences and we should regard the curves shown in Fig. 2.12 only as a qualitative example. It is noted that line shapes, as shown in Fig. 2.12 for a heating rate of 60 Kh" have also been obtained as characteristic curves in model calculations of TPR profiles for three-dimensional phase boundary controlled reactions (topotactic reaction). ... 

Figure 9.7 Temperature-programmed reaction (TPR) spectra for CO oxidation at a series of model catalysts prepared by the soft landing of mass-selected Aun and AunSr cluster ions on MgO(lOO) thin films which are vacancy free (typically 1 % of a monolayer), (a) MgO (b) Au3Sr (c) Au4 (d) Au8. Also shown is the chemical reactivity R of pure Aun and AunSr clusters with 1 < n < 9. (Reproduced from Ref. 21).

The aim of this work was to apply combined temperature-programmed reduction (TPR)/x-ray absorption fine-structure (XAFS) spectroscopy to provide clear evidence regarding the manner in which common promoters (e.g., Cu and alkali, like K) operate during the activation of iron-based Fischer-Tropsch synthesis catalysts. In addition, it was of interest to compare results obtained by EXAFS with earlier ones obtained by Mossbauer spectroscopy to shed light on the possible types of iron carbides formed. To that end, model spectra were generated based on the existing crystallography literature for four carbide compounds of... 

Figure 46 presents the comparison between experimental results (symbols), obtained over a different monolith sample (volume 10cm3) upon performing a TPR run, and the corresponding model predictions (solid lines) 1,020 ppm of NH3 and 960 ppm of NO were fed in a stream of 10% H20, 10% 02, balance nitrogen, with an SV = 36,000 h-1. 

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