Kinetics of oxidative cracking of n‐hexane to olefins over VO_x/Ce‐Al₂O₃ under gas phase oxygen‐free environment

Abstract

The kinetics of oxidative cracking of n‐hexane to olefins using lattice oxygen of VOx/Ce‐Al2O3 is investigated. The TPR/TPO analysis shows a consistent reducibility (79%) of VOx/Ce‐Al2O3 in repeated redox cycles. The total acidity of the sample is found to be 0.54 mmol/g with 22% are strong acid sites that favors olefin selectivity. The oxidative cracking of n‐hexane in a fluidized CREC Riser simulator gives approximately 60% olefin selectivity at 30% n‐hexane conversion. A kinetic model is developed considering (1) cracking, (2) oxidative dehydrogenation (ODH), and (3) catalyst deactivations. The proposed cracking mechanism considers adsorption, C–H and C–C bond fission and desorption as elementary steps and implemented by pseudo steady state hypothesis. A Langmuir‐Hinshelwood mechanism is found to represent the ODH reactions. The developed model fits the experimental data with favorable statistical indicators. The estimated specific reaction rate constants are also found to be consistent with the product selectivity data. © 2016 American Institute of Chemical Engineers AIChE J, 63: 130–138, 2017

Kinetics of Oxidative Cracking of n‐Hexane to Light Olefins using Lattice Oxygen of a VOx/SrO‐γAl2O3 Catalyst

“…The reducible VO x was measured from the amount of hydrogen consumption during TPR (by the numerical integration of the area under the reduction peak). The details of the calculation of the percentage of catalyst reduction are available elsewhere [26,44] . Table 3 shows the amount of hydrogen consumption and the percent reduction of the catalyst samples investigated in this study.…”

“…These are the Eley‐Rideal (ER), Langmuir–Hinshelwood (LH), and Mars‐van Krevleen (MVK) mechanisms [21–25] . For example, Elbadawi et al [26] . applied Langmuir‐Hinshelwood model to study the kinetics of n‐hexane over VO x /Ce‐Al 2 O 3 catalyst.…”

VOX supported on TiO2–Ce0.9Zr0.1O2 core–shell structure catalyst for NH3-SCR of NO

“…The reduction peak area is increased compared with Ce 0.9 Zr 0.1 O 2 , which can be attributed to the effect of superposition of V 5+ , V 4+ and Ce 4+ reduction peaks. 34 The reduction peak of TiO 2 -Ce 0.9 Zr 0.1 O 2 is higher at 544 C than that of Ce 0.9 Zr 0.1 O 2 alone, indicating the interaction between Ce 0.9 Zr 0.1 O 2 and TiO 2 . While the reduction peak of the catalyst supported by TiO 2 -Ce 0.9 Zr 0.1 O 2 is at 566 C, which is higher than that of other catalysts and carriers.…”

Propane Oxidative Dehydrogenation on Vanadium-Based Catalysts under Oxygen-Free Atmospheres

“…This occurs with a gradual increase in the formation of molecular H 2 , which, in turn, slows down the ODH reaction. Therefore, catalyst re-oxidation (regeneration) is necessary for adequate catalyst activity [45,61,96,116,119,120]. Thus, in ODH, periodic catalyst re-oxidations are required and, as a result, the ODH process can be viewed as a system of twin fluidized reactors: an oxidative dehydrogenation reactor and a re-oxidation reactor [12,59,61] (Figure 8).…”