Kinetics of Oxidative Dehydrogenation of <i>n</i>-Butane to C4-Olefins over a VO<sub><i>x</i></sub>/CeO<sub>2</sub>–γAl<sub>2</sub>O<sub>3</sub> Catalyst in Gas-Phase Oxygen-Free Conditions
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Bibliographic record
Abstract
In the present research, the phenomenologically based kinetics of the oxidative dehydrogenation (ODH) of n-butane to C4-olefins over a newly developed VOx/CeO2–γAl2O3 catalyst was investigated. The catalyst was formulated by impregnating 5 wt % V in a 0.2 wt % Ce-modified CeO2–γAl2O3 support. NH3-temperature-programmed desorption indicated the presence of both low- and high-temperature acid sites on the catalyst surface. Temperature-programmed reduction TPR/temperature-programmed oxidation (TPO) analyses showed that 80% of the loaded VOx was available for reduction. The kinetic experiments were carried out in a fluidized CREC Riser Simulator at different reaction temperatures (450–575 °C) and residence times (5–25 s). It was noticed that the highest C4-olefin selectivity of 62% was achieved at 450 °C and a 5 s reaction time. This value decreased with the increase of both reaction temperature and residence time. Two alternative Langmuir–Hinshelwood type kinetics models were formulated considering the cracking, the ODH, and the complete oxidation reactions. The availability of the catalyst oxygen was represented by an exponential decay function of n-butane conversion. The kinetic parameters of the developed models were estimated by fitting the experimental data using MATLAB. Based on goodness of prediction, thermodynamic consistency, and statistical analysis, it was found that the One Adsorption Site Type Langmuir–Hinshelwood model represented the experimental data adequately, with an Akaike information criterion (AIC) of −232. The estimated activation energy for the formation of C4-olefins (90.2 ± 2.8 kJ/mol) was considerably lower than that for the n-butane cracking reaction (105.5 ± 4.7 kJ/mol) as well as that for the complete oxidation to CO2 (121.6 ± 4.2 kJ/mol). On the other hand, the complete oxidation of C2-lumps required a lower activation energy (55.00 ± 2.1 kJ/mol) than the complete oxidation of C4-olefins (81.0 ± 3.2). All these results were consistent with the product analysis data.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.005 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.004 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.003 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it